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Moisture movement within concrete exposed to simulated hotarid/semi-arid conditions

Citation for published version:Alaswad, GA, McCarter, WJ & Suryanto, B 2020, 'Moisture movement within concrete exposed to simulatedhot arid/semi-arid conditions', Construction Materials, vol. 173, no. 6, pp. 298-312.https://doi.org/10.1680/jcoma.18.00012

Digital Object Identifier (DOI):10.1680/jcoma.18.00012

Link:Link to publication record in Heriot-Watt Research Portal

Document Version:Peer reviewed version

Published In:Construction Materials

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Download date: 28. Mar. 2021

Moisture movement within concrete exposed to simulated hot arid/semi-

arid conditions

Author 1: Gasim Alaswad, BSc, MSc

Author 2: William John McCarter, BSc, PhD, DSc, CEng, MICE

Author 3: Benny Suryanto, BEng, MEng, PhD

Author 1: Doctoral Student, School of Energy, Geoscience, Infrastructure and Society,

Institute for Infrastructure and Environment, Heriot Watt University, Edinburgh, EH14 4AS,

UK

Author 2 (corresponding author): Professor, School of Energy, Geoscience, Infrastructure

and Society, Institute for Infrastructure and Environment, Heriot Watt University, Edinburgh,

EH14 4AS, UK.

ORCID: 0000-0002-1949-2856

E-mail: w.j.mccarter@hw.ac.uk

Tel: +44 (0)131 451 3318

Author 3: Associate Professor, School of Energy, Geoscience, Infrastructure and Society,

Institute for Infrastructure and Environment, Heriot Watt University, Edinburgh, EH14 4AS,

UK

ORCID: 0000-0002-3979-9994

Number of Words: 5100

Number of Tables: 6

Number of Figures: 11

Abstract

The ambient environment has considerable influence on the permeation properties of the

near-surface zone of exposed concrete (i.e. the cover zone). Monitoring the mass transport

and flow processes and properties within this region is crucial in evaluating the long-term

performance of concrete for a particular exposure condition. This paper presents an

experimental study on both the spatial and temporal moisture movement within the surface

region of concrete with and without supplementary cementitious materials. Prior to exposure,

the samples were conditioned under two regimes representing poor and good curing; the

samples were then exposed to a simulated hot environment with a diurnal temperature

fluctuation of 20-40C and 60% ambient relative humidity. Moisture movement within the

surface region was monitored using discretized electrical conductivity measurements which,

together with gravimetric measurements, allowed evaluation of the volumetric uptake and

sorptivity of the concrete and the rate and depth of water penetration into the concrete cover-

zone; it is shown that when these are combined, the degree of saturation, effective porosity

and total porosity of the surface region could be estimated. By evaluating the conductivity

prior to and after water absorption, the zone of influence of wetting/drying action (i.e. the

convective zone) could be evaluated.

Keywords: Concrete technology & manufacture / Strength and testing of materials /

Environment

Notation

C = capacitance (pF)

d = depth of penetration of the water front (in mm)

do = depth-based sorptivity coefficient (in mm/h1/2)

f28 = compressive strength at 28 days (MPa)

f180 = compressive strength at 180 days (MPa)

i = cumulative volumetric gain per unit area of inflow surface (mm3/mm2)

io = initial sorption due to the surface effect (mm3/mm2)

k = calibration constant (/cm)

n = saturation coefficient

Rt = thermistor resistance (ohms)

Rc = concrete resistance (ohms)

Sd = depth-based sorptivity coefficient (in mm/h1/2)

Sv = sorptivity based on the volumetric uptake by the concrete

Sr = degree of saturation (%0

t = elapsed time (h)

tm = time of arrival of water-front at electrodes (h)

T = temperature (ºC)

w/b = water-binder ratio

, and = thermistor coefficients (K-1)

= conductivity (S/cm)

o = conductivity just prior to water absorption (S/cm)

ss = conductivity at steady-state (S/cm)

t = conductivity at time, t, after the start of the absorption test (S/cm)

ϕeff = effective porosity (%)

ϕ = capillary porosity (%)

1. Introduction

The movement of water (and water containing dissolved ions) into the cover region of

reinforced concrete plays a significant role in virtually all deterioration processes; for

example, chloride ingress, alkali-silica reaction, carbonation and sulphate attack all depend

on the availability of water. Reinforcement corrosion, either through chloride attack or

carbonation, is considered one of the main causes of the premature deterioration of concrete

structures (Jones et al, 1997). The in-service performance and long-term durability of

concrete is influenced by a number of factors, for example, the quality of construction

materials; quality control in the manufacturing and placement of concrete; poor construction

practices, such as unskilled labour or unqualified supervision; severe climate with large

diurnal temperature fluctuations and the lack of construction standards and specifications

relevant to local environments. In connection with corrosion, as it is the concrete cover which

protects the steel from the ambient environment it is not surprising that the protective

qualities of this zone of concrete have a considerable bearing on concrete performance and

durability. In addition, the use of supplementary cementitious materials (SCM) to form

blended cements are now being increasingly utilized to improve concrete durability.

Regarding durability, in addition to a specified strength requirement, it is the permeation

properties of the cover-zone concrete which determine concrete performance and terms such

as diffusivity, permeability and sorptivity are used in this respect. The service life of

reinforced concrete structures is largely determined by the surface 50-100mm, and an

understanding of water and moisture movement within this zone is crucial in developing

guidelines and performance-based specifications for concreting operations in different

environmental conditions. Measures implemented for concrete performance need to consider

the particular ambient environment prevailing in a country or region as hot-humid climates

will have totally different performance specifications from, for example, cool temperate

climates.

1.1 Background and Context

The cover-zone of concrete exposed to cyclic wetting and drying action will fluctuate

between fully saturated and partially saturated states which will establish moisture gradients

through this region. Water and moisture movement will thus be a combination of both water

absorption by capillarity and water-vapour diffusive processes. It is not surprising, therefore,

that the water absorption properties of a concrete surface have been used to index concrete

performance and numerous surface-applied tests have been developed in this respect which

include, surface absorption tests (BSI 1996; Wilson et al. 1998; ASTM 2013); Figg

hypodermic methods (Figg 1973); water permeability tests (Basheer 1993); the covercrete

absorption test (Dhir et al. 1987; Meletion et al. 1992; Blight and Lampacher 1995);

cumulative absorption and sorptivity methods (Hall and Yau 1987; McCarter 1993; Classie et

al. 1999; BSI 2011) and the Clam/Autoclam permeation tests (Basheer et al. 1995; Basheer

and Nolan 2001; Yang et al. 2015). These tests quantify the cumulative volumetric uptake of

the concrete surface, however, no information is given on the depth or the rate of penetration

of the water-front into the surface region. Furthermore, evaporative processes are equally as

important as wetting, yet have not received the same attention. A total assessment of the

quality of the surface region should not only consider the drying and wetting response but

also allow evaluation of the spatial distribution of moisture within the concrete during drying

and wetting processes.

Regarding the evaluation of the depth of penetration of the water-front, as yet, there are no

standardized procedures. The most straightforward approach is to subject replicate samples to

a water absorption test, which are then split at specified times and the depth of water

penetration measured. It has been reported, however, that as the strength of the concrete

increases, visual detection of the waterfront can present considerably difficulty (McCarter et

al. 1992). It has been shown that the depth of penetration approximates to a square-root-time

relationship (Ho and Lewis 1984; McCarter et al. 1992) viz,

d = Sd t + do (1)

where d is the depth of penetration of the water front (in mm), t is the elapsed time (in h), do

is a constant (in mm) and Sd is a depth-based sorptivity coefficient (in mm/h1/2). There is a

paucity of data on the depth of water penetration into concrete, for example: Sd values for

concretes subjected to different conditioning procedures were found to be in the range 1.5-

19mm/hr1/2 (Ho et al. 1989) with absorption tests of 24-hours duration and concrete

compressive strengths in the range 30-33MPa; Sd values for plain Portland cement concrete

mixes with strengths in the range 36-59MPa, based on a 24-hour water absorption test, were

reported as being in the range 2.2-4.7mm/h1/2 (McCarter et al. 1992).

It is set against this background that the current study investigates both the spatial and

temporal variations in moisture within the surface region of concrete in response to external

changes in hygrothermal conditions viz. cyclic temperature changes to simulate diurnal

temperature variations experienced in hot arid/semi-arid climates. It must be emphasised,

however, that the temperature regime adopted within this study does not purport to represent

all the climatic conditions experienced in such regions. This study also investigates the

influence of curing conditions and SCM's on the response of the cover-zone to such

environmental action. This is achieved through the use of both gravimetric measurements and

discretized electrical conductivity measurements, the latter being evaluated through the use of

an array of embedded electrodes. Through this combined test-method approach, it is shown

that a number of important parameters related to the long-term performance of concrete can

be estimated.

2. Experimental Programme

In order to monitor both the temporal and spatial changes in moisture movement both in the

short- and long- term, a test-cell was designed such that electrical measurements (resistance

in this instance) and temperature could be made at discrete depths from the exposed surface

of the concrete samples thereby allowing an integrated assessment of the surface-zone. In

parallel, the cumulative volumetric water uptake by the exposed concrete surface and internal

relative humidity (RH) were also monitored.

2.1 Samples

In the current study, the binders comprised ordinary Portland cement clinker, CEM I 52.5N to

EN197-1 (BSI 2011); CEM I cement blended with ground granulated blast-furnace slag to

EN15167-1 (BSI 2006a) and CEM I cement blended with a low-lime fly-ash to EN450-1

(BSI 2012). The oxide analysis of the cementitious materials is given in Table 1 and the

concrete mixes are presented in Table 2, together with their respective 28-day (f28) and 180-

day (f180) compressive strengths after continuous submerged curing at 21C±1°C.

A crushed rock (granite) coarse aggregate and matching crushed rock fines were used

throughout. For the fine aggregate, 100% passed the 5mm sieve, 8% passed the 150m sieve;

additional coarse and fine aggregate properties are presented in Table 3 conducted in

accordance with BS-EN 1097-3 (BSI 1998), BS-EN 1097-6 (BSI 2013) and BS 812-112 (BSI

1990). The aggregate was conditioned to a saturated surface dry state. The aggregate content

was adjusted to ensure that the mass of binder remained constant for each water-binder (w/b)

ratio. Batches were initially dry mixed in a pan mixer for one minute to ensure thorough

mixing of replacement materials prior to addition of water. The following were cast for each

mix: six samples placed in cylindrical test-cells (detailed below) for moisture, relative

humidity and gravimetric monitoring and three, 100mm cubes for compressive strength tests.

The range of mixes used within the experimental programme, in terms of binder-content,

binder composition and water-binder ratio, would satisfy minimum requirements specified in

BS 8500-1 (BSI 2006b) for environmental exposure classes XC (corrosion induced by

carbonation), XS (corrosion induced by chlorides from sea-water) and XD (corrosion induced

by chlorides other than sea-water e.g. deicing salt) for an intended working life of 100 years,

with 50mm cover-to-steel.

2.2 Test Cells

Concrete samples were cast in 182mm (outside diameter) and 200mm (high) PVC moulds.

One end of the cylinder was attached to 12mm plywood base-plate and the concrete surface

cast against the plywood was used as the working surface; the plywood had been given a coat

of proprietary release-agent prior to casting. Pairs of stainless steel rod-electrodes, were

inserted through the side of the mould shown schematically in Figure 1. The rod-electrodes

were 2.6mm in diameter and sleeved to expose a 20mm tip. Within each electrode pair,

electrodes were positioned at 12mm centre to centre (c/c) and protruded 50mm into the

sample. With reference to Figure 1, five electrode-pairs were positioned at 10mm intervals

from the working surface with a 30 offset; a pair of electrodes was also positioned at 100mm

and at 175mm from the working surface. This is a variation on other electrode configurations

(Schiessl and Raupach 1996; Rajabipour et al. 2005; McCarter et al. 2015) causing less

interference with the natural distribution of aggregate within the sample. The electrode-pairs

within the test-cell were calibrated by filling the cell with a solution of known conductivity;

hence, if cal is the conductivity of the calibrating solution (calcium hydroxide) and Rcal the

measured resistance across the electrode-pair, then

𝜎𝑐𝑎𝑙 =𝑘

𝑅𝑐𝑎𝑙 (2)

where k is the (geometrical) calibration constant for the electrode-pair. However, as the test-

cell had five (geometrically similar) electrode pairs, an average value of k was evaluated to

give an overall test-cell constant for the electrodes; the value of k was obtained as 0.306 cm-1

(±5%). This allowed the concrete resistance, Rc (ohms), measured across the electrodes to be

converted to conductivity, (S/cm), by,

)cm/S(cR

k (3)

In addition to the electrodes, four, 12mm diameter (50mm long) cavities were formed to

allow relative humidity measurements. The centres of the cavities were positioned at 25, 50,

100, and 175mm from the working surface, as with the electrodes, the cavities had a 30

offset. Pre-formed cavities were chosen in preference to drilled holes due potential damage

caused by hammer-action drilling, particularly those cavities close to the test surface. The

inside of each cavity was lined with a thin plastic sleeve (Kim and Lee 1999; Holmes and

West 2013; Granja et al. 2014) with the end of the cavity exposed to ensure that the RH was

representative of the concrete at that depth. A RH sensor was inserted within each cavity

which was then sealed with a tightly fitting rubber bung.

Two thermistors (for temperature measurements) were cast into the sample and were attached

to electrodes positioned at 10mm and 100mm from the exposed surface.

2.3 Ambient Temperature and Curing Regimes

After casting and compacting, the top (cast) surface of each cell was tightly covered with a

plastic sheet so as to prevent evaporation. The cylinders were immediately placed in an

environmental cabinet which was programmed to give a 24-hour temperature cycle of: 10-

hours at 40±1C, 3-hours cooling to 21C followed by 11-hours at 21±1C (see Figure 2)..

The RH was maintained at 60% over a saturated sodium bromide solution with the air speed

over the samples maintained at approximately 4m/s. As noted earlier, although it is difficult

to generalise diurnal temperature fluctuations and ambient humidity which can be

experienced in hot-arid/semi-arid countries (see, for example, Baghabra Al-Amoudi et al.

2004; Ait-Aider et al. 2007; Haque et al 2007; Pattanaik et al. 2015), the regime adopted thus

represents a specific set of environmental conditions. The samples exposed to this regime

from casting and throughout the testing programme. After 24-hours, the cast surface was

sealed with two coats of a high-build epoxy paint; also, while the final coat of epoxy was still

tacky, it was covered with a layer of cling-film to add an additional vapour barrier to ensure

no moisture movement through this surface.

Each set of six replicates was further sub-divided into two groups of three samples. Each

group was subjected to a specific curing regime:

(i) C1 curing, representing good curing: the plywood was maintained in place for 14 days.

Note: the concrete cast against the plywood formed the working surface.

(ii) C2 curing, representing poor curing: after 24-hours the plywood was removed.

The PVC moulds were maintained in place throughout the testing programme which ensured

uniaxial moisture movement; the samples also remained in the environmental cabinet

throughout and subjected to a wetting cycle of 24-hours duration. In the current work,

samples were subject to a wetting cycle every 60-days (approximately) which allowed

sufficient time for natural drying of the concrete under the simulated environmental

conditions.

2.4 Measurements and Data Acquisition

The electrical resistance (Rc in ohms) of the concrete between each pair of electrodes was

obtained employing a two-point technique using signal amplitude of 350mV at a frequency of

1kHz. This frequency was optimised from a-priori experiments using multi-frequency

measurements (impedance spectroscopy) to ensure electrode polarization effects were

reduced to a minimum (McCarter and Brousseau 1990). The cabling from the cells was

ducted out through a small porthole in the side of the chamber and connected to a resistance

meter and multiplexing unit to record the electrical resistance across the electrode-pairs and

thermistors. A reading cycle, comprising seven electrode-pair measurements and three

thermistor measurements (two embedded within sample and one placed in the environmental

cabinet), was initiated every 2 minutes over the 24-hour absorption cycle.

Thermistor measurements were converted to temperature using the Steinhart-Hart equation,

T = [ + lnRt + (lnRt)3]-1 - 273.15 (4)

where Rt is the measured resistance of the thermistor (ohms); , and are coefficients

which depend on the type of thermistor and in the current work were (Betatherm 2014),

respectively, 1.29×103K-1, 2.36×10-4K-1 and 9.51×10-8K-1and T is the computed temperature

(in ºC ± 0.2°C).

Measurement of the volumetric uptake of the concrete samples during water-absorption was

obtained by filling the Plexiglas cap via a burette until water weeped out of the small hole in

the cap. The supply of water from the burette was then shut and water was absorbed from the

reservoir of water in the cap; at specified times, the burette was opened and the volume of

water required to refill the reservoir recorded from the burette (±0.1ml). Absorption

measurements were taken when the sample was at the constant laboratory temperature regime

of the heating/cooling cycle (i.e. 21±1C). The complete testing arrangement is shown in

Figure 3.

The RH in the cavity was recorded using a capacitive humidity sensor, with the sensor

permanently mounted in each cavity. A LCR meter, operating at a frequency of 10kHz and

350mV signal amplitude, was used to measure the capacitance (C, in pF), which was,

subsequently, converted to %RH (±2%) using the equation (Humirel 2002),

%RH = [-8.8932×10-4×C3] + [0.4651×C2] – [77.970×C] +4202 (5)

3. Results and Discussion

The combination of internal conductivity and gravimetric water-uptake measurements are

presented to highlight the range of parameters which can be evaluated from the dual testing

protocol and highlights the influence of external environment, curing and supplementary

cementitious material (SCM) on water and moisture movement within the surface-zone

(100mm).

3.1 Water Absorption

For illustrative purposes, Figure 4(a)-(c) presents the change in the electrical conductivity of

the concrete during water absorption for the concrete mixes (water/binder ratio, w/b = 0.6)

under curing regime C2. As conductivity values at the different electrode positions can

change by more than an order of magnitude during water absorption, this Figure presents the

relative change in conductivity, o/t , where t is the conductivity at time, t, after the start of

the absorption test and o is the conductivity just prior to the application of water at the

surface. As the water-front moves through the surface zone t will increase and the response

at a particular electrode-pair is characterised by a well-defined, decreasing portion although it

is evident that the gradient of this region becomes flatter (i.e. becomes more negative) with

increasing depth from the surface. The decreasing portion of the curve indicates the arrival of

the water-front into the electrical field between that particular electrode-pair; once the water-

front has moved beyond the electrical field, a steady-state ratio is achieved and denoted

o/ss, where ss is denoted the steady-state conductivity. It could be assumed that at steady-

state, the concrete is in a fully saturated state in the vicinity of the electrode-pair.

A sigmoidal decay curve can be used to describe the o/t versus time (t) response viz.,

s]tg[t

101

c

t

o

m

(6)

The above equation also allows a means of standardising the way in which features of the

response can be quantified. In this equation, c is a constant which ensures that when t = 0,

o/t = 1.0; as t , s is the steady-state ratio,o/ss; g controls the gradient of the

descending portion of the response – as the value of g increases the slope gets more

precipitous; tm represents the time at which d(o/t)/dt maximises on the decreasing portion

of the o/t response. Again, as way of illustration, Figure 4(d) presents four best-fit curves

the form of equation (6) for the response presented in Figure 4(a) over the surface 40mm,

with the values for the modelling parameters c, g, tm and s presented in Table 4. From

equation (5) above, it is proposed that the time of arrival at the depth of the electrode pair

occurs at time, tm, when d(o/t)/dt maximises. The sharpness of the advancing water-front

would be related to the parameter, g; as g decreases, it may imply that the advancing water-

front moves from a sharp wet-front (see, for example, Figure 4(a) at 10mm depth) to one

which becomes increasingly more diffuse with depth as absorption proceeds (see Figure 4(a)

at 40mm depth).

Regarding the steady-state parameter, s, this will be related to the degree of capillary pore

saturation just prior to the start of the absorption test i.e. the residual moisture profile through

the surface region resulting from the preceding drying cycle. With reference to Figure 5, if

concrete (of capillary porosity, ) can be considered as a three-phase system comprising air,

pore-water and solids (i.e. aggregate, products of hydration and unhydrated cement) then, as

the initial degree of pore saturation (Sr) increases, the volume of accessible capillary pore

space (i.e. the effective porosity, eff) which can be filled by the advancing water-front is

reduced. From an electrical point of view, this will imply that the difference between the

conductivity measured at the start of the absorption test, o in Figure 5(a), and its steady-state

value, ss in Figure 5(b), will reduce with increasing degree of initial pore saturation; in terms

of the steady-state parameter, s (= o/ss), this will increase with increasing degree of initial

pore saturation, Sr. With reference to the responses presented in Figure 4(a)-(c), where a

steady-state o/ss value has been achieved, it is evident that this is, indeed, the case as its

value increases with increasing depth from the exposed surface or, in qualitative terms, the

degree of saturation increases with depth from the exposed surface prior to the start of the

absorption test.

It is interesting to note that a saturation function has been presented which relates the

electrical properties of cement-based materials to their degree of saturation (Weiss et al.

2012; Wang et al. 2016). Using the notation defined above, and adapting the work by Weiss

et al (2012), the following relationship has been presented,

𝑆𝑟 = (𝜎𝑜

𝜎𝑠𝑠)

1

𝑛 × 100% (7)

where n is defined as the saturation coefficient. Values of n have been reported in the range

3.5-5.5 (Nokken and Hooton, 2008; Weiss et al. 2012) with a value of 4.0 (Weiss et al. 2012)

suggested for plain Portland cement-based systems. Consider, for example, the steady-state

o/ss values for the PC concrete in Figure 4(a): at 10mm = 0.083; 20mm = 0.26; 30mm =

0.39 and 40mm = 0.43. If a value of n = 4.0 is assumed, this would evaluate the degree of

saturation, Sr, of the concrete just prior to the start of the absorption test as: at 10mm = 54%;

20mm = 71%; 30mm = 79% and 40mm = 81%. Clearly more work is required in establishing

values for n for different concretes with and without SCMs, as this would allow a simple

means of estimating Sr gradients through the surface zone.

It is interesting to note that some of the responses displayed an initial increase in resistance

on application of water at the surface of the samples (i.e. o/t > 1.0) before decreasing. This

feature is particularly evident in Figure 4(c) for the GGBS concrete mix. As the resistance

over this time has increased, a possible explanation of such a feature would be as a result

from air dispersing into the capillary pores in the vicinity of the electrodes: as the water from

moves into the partially saturated concrete, a volume of air will be pushed ahead of the

advancing the water-front which disperses into the pore system which, in this instance, is

sufficient to cause a transitory increase in resistance. Further work is required, however, to

fully explain this feature.

3.2 Water Penetration and Volumetric Gain

Using the definition of tm defined above to estimate the time of arrival of the water-front at an

electrode-pair, Figures 6(a) and (b) present the water penetration depth within the initial 16

hours of the absorption cycle and plotted in the form of equation (1). Error bars on the data

markers represent ±1.0 standard deviation, where the error bars appear to be missing, the data

marker is larger than the error bar. This has only been undertaken for C1 and C2 cured

concrete mixes having w/b = 0.6 as the water-front had not penetrated sufficiently within the

24-hour absorption period for w/b = 0.4 mixes to enable a relationship to be established.

Regarding samples with w/b = 0.4, for C1 cured samples, the depth of water penetration was,

typically, 20mm and for C2 cured samples 30mm. This, in itself, highlights the influence

of w/b ratio on water ingress for the curing and exposure conditions detailed above.

When using SCM's good curing, particularly during the early stages of strength development,

is essential to ensure that water remains within the capillary pore structure due to the much

slower pozzolanic reaction. This is clearly highlighted in Figure 6(b) whereby C2 curing in

the simulated climatic conditions results in a rapid movement of water through the surface

50mm as depth-based sorptivity values (Sd) have increased when compared to their C1

cured counterparts (Figure 6(a)). Particularly striking is the FA concrete mix where the Sd

value has increased by more than 150%; furthermore, the high replacement GGBS mix gives

the highest Sd values under both curing regimes whereas the PC mix performs best at this w/b

ratio under both C1 and C2 curing. Generally, there is good repeatability and only the C1

cured FA mix displays scatter at depths of 30mm and 40mm.

Figure 7(a)-(b) shows the cumulative volumetric gain per unit area of inflow surface (i,

mm3/mm2) for all concretes during the initial 6 hours absorption with the values at 24-hours

presented in Table 4. The data have been plotted on a square-root-time axis and it is evident

that the best-fit line takes the form,

i = Sv t + io (8)

where Sv is the sorptivity based on the volumetric uptake by the concrete and io is the initial

sorption due to the surface effect. Considering the Sv values (presented in Figure legend) and

the 24-hour cumulative absorption (Table 5), the concretes containing GGBS and FA

outperform the plain PC mixes when used at the low w/b ratio (0.4) with C1 curing; however,

this reverses when these concretes are used at w/b = 0.6 with C2 curing.

The depth of penetration of the water-front, d (in mm), and the volumetric gain of the

concrete, i (in mm3/mm2) can be combined to estimate the effective porosity, eff, of the

surface region. As noted above, the effective porosity represents the fraction of empty (or air-

filled) capillary pores within the binder just prior to the start of water absorption (see Figure

5) and is the void space that can be invaded by the advancing water-front, hence,

%100d

ieff

(9)

For example, consider Figure 8 which presents the depth of penetration and volumetric gain

results for the FA concrete with w/b = 0.6 under C2 curing: when the water-front, d, has

penetrated to 30mm, the volumetric gain at this time is 1.17 mm3/mm2, hence eff for the

surface 30mm is 3.9%. In this way, the effective porosity of the surface region could be

estimated and, when combined with the degree of saturation, Sr, discussed above in relation

to the steady-state conductivity ratio, o/ss , the total porosity, , of the surface region could

then be evaluated i.e. = eff/(1-Sr).

This combination of techniques offers a methodology for studying and evaluating the depth-

related features which, ultimately, are of considerable important in relation to concrete

performance.

3.3 Conductivity profiles and the Convective Zone

As water evaporates from (or is absorbed into) the concrete surface, a moisture gradient will

be established through the concrete cover-zone. As the electrical conductivity of the concrete

will be directly related to the volumetric water-content (or the degree of saturation) of the

capillary pore network, the conductivity profile through the sample should mimic the

moisture gradient. As way of illustration, Figures 9-11 present the conductivity profiles

through the concrete samples both before and after water absorption for two cycles of

drying/wetting. As water is absorbed into the concrete, it is evident that the conductivity after

the 24-hour absorption cycle has increased relative to the value before absorption. This

simply reflects the influence of the advancing water-front; however, it is also noticeable that

this effect diminishes with increasing depth from the concrete surface. It could be postulated

that, where the conductivity of the concrete remains unaltered before and after absorption,

this would indicate the maximum potential extent of the zone most influenced by

drying/wetting action i.e. the convective zone. The convective zone, or influential depth of

moisture transport (Li et al. 2009), would lie within a range bounded by the depth at which no

change in conductivity is observed at the electrode-pair, and the electrode-pair positioned

above. As the absorption period is 24-hours, any hydration and pozzolanic reaction occurring

in this time will have negligible influence on the conductivity of the concrete and changes in

conductivity will be solely due to the moisture-state of the capillary pore system. The

influence of curing regime, w/b ratio and SCM, coupled with the environmental exposure

conditions, is clearly evident from these Figures with, in some cases, the convective zone

extending through the surface 100mm (see, for example, Figure 11(d)).

For those mixes with w/b = 0.4 and C1 or C2 curing regimes, the conductivity values at

electrode positions 50mm, 100mm and 175mm are, in most cases, within ±10% of the mean

of the two respective values. This would imply that the curing regime applied at the surface

does not have any significant influence on the concrete at these depths where the concrete is

virtually self-curing. Considering the conductivity profiles between the 1st and 2nd absorption

cycles, it is also apparent that they become displaced downwards indicating a decrease in

conductivity over the intervening period. This decrease can be attributed to ongoing

hydration and pozzolanic reaction which modifies the microstructure resulting in a more

tortuous/disconnected pore network. Considering the electrodes positioned at 100mm from

the surface, at the end of the 2nd absorption cycle mixes with SCMs exhibit conductivity

values which are, typically, 2.5-3.0 times lower than the respective PC mix, regardless of w/b

ratio or curing regime.

For comparative purposes, Table 6 presents the relative humidity at cavities positioned at 25,

50, 100 and 175mm from the concrete surface for C1 and C2 curing. It was observed that the

RH sensor had a relatively slow response to changes in moisture state of the concrete, whilst

the electrical conductivity responded more rapidly. As can be seen from Table 6 (C1 curing

regime) the RH at 25mm and 50mm displays an increase for all mixes; for C2 curing,

however, mixes with w/b = 0.6 display an increase in humidity extending to 100mm. Whilst

there are similarities between the conductivity profile and RH profile, it must be emphasised

that conduction through the specimens will be directly related to the degree of saturation of

the aqueous phase in the capillary pore network, whereas RH is related to the water vapour

present in the air within the preformed cavity.

4. Conclusions and Concluding Comments

A combined testing procedure, using gravimetric and discretized, in-situ, conductivity

measurements, was used to study both the spatial and temporal distribution of moisture

within the surface 175mm of concrete samples. Concrete mixes, with and without SCMs,

were subjected to a simulated ambient environment which was representative of an arid/semi-

arid region. The work has clearly highlighted and quantified the influence of w/b ratio and

curing on the permeation properties of blended systems exposed to diurnal fluctuations in

temperature during the post-placement phase of concreting operations. For the curing and

simulated temperature and humidity regime used in the current study, it was observed that,

Under the environmental exposure regime, the influence of C1 curing and C2 curing on

both the volumetric-gain sorptivity (Sv) and the depth-related sorptivity (Sd) was clearly

evident. When the concrete is cured at a condition in which sufficient moisture is

retained within the capillary pore network, as in the case with C1 curing, both sorptivities

are significantly improved relative to C2 curing.

The incorporation of SCMs can beneficially reduce volumetric gain and depth of

penetration with the proviso that, under the environmental exposure conditions, these

materials are used in conjunction with a low w/b ratio (=0.4) and C1curing. Due to the

slow pozzolanic reaction, mixes containing SCMs with a high w/b ratio (0.6) and C2

curing resulted in the highest volumetric gain and rate/depth of water penetration

Electrical measurements taken at discrete depths from the exposed concrete surface

showed that during absorption, the penetration of water into concrete could be modelled

by a sigmoidal curve and indicated that the advancing water-front became increasingly

more diffuse with depth.

The depth of water penetration (d) together with the cumulative volumetric water gain of

the concrete, i (mm3/mm2), could be combined to estimate of effective porosity of the

surface zone.

The convective zone can be estimated by evaluating the conductivity profile through the

surface zone prior to and after water absorption. It was shown that the convective zone

extended over the surface 50-100mm when the concrete with the high w/b ratio was

subjected to C2 curing; concrete at greater depths is virtually self-curing. The RH profile,

although showing similar trends to the conductivity profiles, did not have the same level

of precision (or response rate) in estimating the convective zone.

The testing methodology presented offers the potential in evaluating a range of parameters

which are important in relation to the long-term performance of concrete; furthermore, as

measurements are taken at discrete locations within the concrete cover, it allows an integrated

assessment of this region. For example, it was shown that through the use of a saturation

function, the steady-state conductivity-ratio could be used to estimate the degree of saturation

of the concrete and, when this was combined with the effective porosity, the total porosity

could be evaluated.

Acknowledgements

One of the Authors (GA) would like to thank Libyan Embassy-Cultural Attaché for their

financial support (Grant Reference 11049).

Conflict of Interest

The authors declare that they have no conflict of interest.

References

Ait-Aider H,_Hannachi NE and Mouret M (2007) Importance of W/C ratio on compressive

strength of concrete in hot climate conditions. Building and Environment 42(6): 2461-2465.

doi: 10.1016/j.buildenv.2006.05.003

ASTM C1585-13 (2013) Standard Test Method for Measurement of Rate of Absorption of

Water by Hydraulic-Cement Concretes. ASTM International, West Conshohocken, PA.

Baghabra Al-Amoudi OS, Maslehuddin M and Abiola TO (2004) Effect of type and dosage

of silica fume on plastic shrinkage in concrete exposed to hot weather. Construction and

Building Materials 18(10): 737-743. doi: 10.1016/j.conbuildmat.2004.04.031

Basheer PAM and Nolan E (2001) Near-surface moisture gradients and in situ permeation

tests. Construction and Building Materials 15(2/3): 105-114. doi 10.1016/S0950-

0618(00)00059-3

Basheer PAM (1993) A brief review of methods for measuring the permeation properties of

concrete in situ. Proceedings of the Institution of Civil Engineers - Structures and Buildings

99(1): 74-83. doi: 10.1680/istbu.1993.22515

Basheer PAM, Montgomery FR and Long AE (1995) CLAM tests for measuring in-situ

permeation properties of concrete. Nondestructive Testing and Evaluation 12(1): 53-73. doi:

10.1080/10589759508952835

BetaTHERM NTC Thermistor Datasheet (http://beta.dk/wp-

content/uploads/2014/11/teoridel.pdf accessed 26/04/2018).

Blight GE and Lampacher BJ (1995) Applying covercrete absorption test to in-situ tests on

structures. ASCE Journal of Materials in Civil Engineering 7(1): 1-8. doi:

10.1061/(ASCE)0899-1561(1995)7:1(1)

British Standards Institution (BSI) BS 1881-208 (1996) Testing Concrete. Recommendations

for the determination of the initial surface absorption of concrete. BSI, London, UK.

British Standards Institution (BSI) BS-EN 1097-3 (1998) Tests for mechanical and physical

properties of aggregates - Part 3: Determination of loose bulk density and voids, BSI,

London, UK.

British Standards Institution (BSI) BS 812-112 (1990) Testing Aggregates. Methods for

determination of aggregate impact value (AIV). BSI London, UK.

British Standards Institution (BSI) BS-EN15167-1 (2006a) Ground granulated blast furnace

slag for use in concrete, mortar and grout - Part 1: Definitions, specifications and conformity

criteria. BSI, London, UK.

British Standards Institution (BSI) BS8500-1 (2006b) Concrete-Complementary British

Standard to EN 206-1 – Part 1: Method of specifying and guidance for the specifier. BSI,

London, UK.

British Standards Institution (BSI) BS 1881-122 (2011) Testing Concrete. Method for

determination of water absorption. BSI London, UK.

British Standards Institution (BSI) BS-EN197-1 (2011) Cement-Part 1: Composition,

specifications and conformity criteria for common cements. BSI, London, UK.

British Standards Institution (BSI) BS-EN450-1 (2012) Fly ash for concrete. Definition,

specifications and conformity criteria. BSI, London, UK.

British Standards Institution (BSI) BS-EN 1097-6 (2013) Tests for mechanical and physical

properties of aggregates - Part 6: Determination of particle density and water absorption, BSI,

London, UK.

Classie PA, Elsayad HI and Shaaban IG (1999) Test methods for measuring fluid transport in

cover concrete. ASCE Journal of Materials in Civil Engineering 11(2): 138-143. doi:

10.1061/(ASCE)0899-1561(1999)11:2(138)

Dhir RK, Hewlett PC and Chan YN (1987) Near-surface characteristics of concrete:

assessment and development of in situ test methods. Magazine of Concrete Research

39(141): 183-195. doi: 10.1680/macr.1987.39.141.183

Figg, J.W., (1973). ‘Methods for measuring the air and water permeability of concrete.’

Magazine of Concrete Research 25(85): 213-219. doi: 10.1680/macr.1973.25.85.213

Granja JL, Azenha M, de Sousa C, Faria R. and Barros J (2014) Hygrometric assessment of

internal relative humidity in concrete: practical application issues. Journal of Advanced

Concrete Technology, 12(August): 250-265. doi: 10.3151/jact.12.250

Hall C and Yau MHR (1987) Water movement in porous building materials - IX: the water

absorption and sorptivity of concretes. Building and Environment 22(1): 77-82. doi:

10.1016/0360-1323(87)90044-8

Haque MN, Al-Khaiat H and John B (2007) Climatic zones - A prelude to designing durable

concrete structures in the Arabian Gulf. Building and Environment 42(6): 2410-2416. doi:

10.1016/j.buildenv.2006.04.006

Ho DWS and Lewis RK (1984) Concrete quality as measured by water sorptivity.

Transactions of the Institution of Engineers, Australia CE26(4): 306-313.

Ho DWS, Cui QY and Ritchie DJ (1989) The influence of humidity and curing time on the

quality of concrete. Cement and Concrete Research 19(3): 457-464. DOI: 10.1016/0008-

8846(89)90034-3

Holmes N and West RP (2013) Enhanced accelerated drying of concrete floor slabs.

Magazine of Concrete Research 65(19): 1187-1198. doi: 10.1680/macr.13.00142

Humirel (2002) Technical Data sheet for HS1100/HS1101 relative humidity sensor, June

(https://www.parallax.com/sites/default/files/downloads/27920-Humidity-Sensor-

Datasheet.pdf accessed 24/04/2018).

Jones AEK, Marsh B, Clark L, Seymour D, Basheer P and Long A (1997) Development of a

holistic approach to ensure the durability of new concrete construction BCA Research Report

C/21, British Cement Association, Camberley, UK, 1-81

Kim JK and Lee CS (1999) Moisture diffusion of concrete considering self-desiccation at

early ages. Cement and Concrete Research 29(12): 1921-1927. doi: 10.1016/S0008-

8846(99)00192-1

Li K, Li C and Chen Z (2009) Influential depth of moisture transport in concrete subject to

drying–wetting cycles. Cement and Concrete Composites 31(10): 693-698. doi:

10.1016/j.cemconcomp.2009.08.006

McCarter WJ (1993). Influence of surface finish on sorptivity of concrete. ASCE Journal of

Materials in Civil Engineering 5(1): 130-136. doi: 10.1061/(ASCE)0899-

1561(1993)5:1(130)

McCarter WJ and Brousseau R (1990) The A.C. response of hardened cement paste. Cement

and Concrete Research 20(6): 891-900. doi: 10.1016/0008-8846(90)90051-X

McCarter WJ, Chrisp T, Starrs G, Basheer PAM, Nanukuttan S, Srinivasan S and Magee B

(2015) A durability performance-index for concrete: developments in a novel test method.’

International Journal of Structural Engineering 6(1): 2-22. doi:

10.1504/IJSTRUCTE.2015.067966

McCarter WJ, Ezirim H and Emerson M (1992) Absorption of water and chloride into

concrete. Magazine of Concrete Research 44(158): 31-37. doi: 10.1680/macr.1992.44.158.31

Meletion CA, Mang T and Bloomquist D (1992) Development of a field permeability test

apparatus and method for concrete. American Concrete Institute Materials Journal 89(1): 83-

89.

Nokken MR, Hooton RD (2008) Using pore parameters to estimate permeability or

conductivity of concrete, Mater. Struct, 41(1): 1-16. doi: 10.1617/s11527-006-9212-y

Pattanaik SC, Gopalkrishnan E and Patro S. (2015) A study on deterioration of reinforced

cement concrete structures in Mumbai. Indian Concrete Journal, 89(May): 51-58.

Rajabipour F; Weiss J, Shane JD, Mason TO and Shah SP (2005) Procedure to interpret

electrical conductivity measurements in cover concrete during rewetting. ASCE Journal of

Materials in Civil Engineering 17(5): 586-594. doi: 10.1061/(ASCE)0899-

1561(2005)17:5(586)

Schiessl, P. and Raupach, M., (1996). ‘Instrumentation of structures with sensors – why and

how?’ Proceedings Concrete in the Service of Mankind Conference: Concrete Repair,

Rehabilitation and Protection (Eds. R.K. Dhir and M.R. Jones), Dundee, 27-28 June, 1-15

(ISBN 0 419 21490 9).

Wang Y, Gong F, Zhang D and Ueda T (2016) Estimation of ice content in mortar based on

electrical measurements under freeze-thaw cycle. Journal of Advanced Concrete Technology,

14(February): 35-46. doi: 10.3151/jact.14.35

Weiss J, Snyder K, Bullard J and Bentz D (2013) Using a Saturation Function to Interpret the

Electrical Properties of Partially Saturated Concrete. ASCE Journal of Materials in Civil

Engineering 25(8): 1097-1106. doi: 10.1061/(ASCE)MT.1943-5533.00005494

Wilson MA, Taylor SC and Hoff WD (1998) The initial surface absorption test (ISAT): an

analytical approach. Magazine of Concrete Research 50(2):179-185. doi:

10.1680/macr.1998.50.2.179

Yang K, Basheer PAM, Magee B, Bai Y and Long AE (2015) Repeatability and reliability of

new air and water permeability tests for assessing the durability of high-performance

concretes. ASCE Journal of Materials in Civil Engineering 27(12): 04015057. doi:

10.1061/(ASCE)MT.1943-5533.0001262

Captions for Figures

Figure 1 Schematic diagram showing positioning of electrodes, humidity cavities and

thermistors within the test cell (a) sectional view, and (b) plan view.

Figure 2 Thermal cycling regime within environmental chamber (RH=60%).

Figure 3 Water absorption and monitoring arrangement.

Figure 4 Relative change in conductivity o/t for C2 cured concrete mixes (w/b = 0.6)

during the initial 24-hour absorption cycle for (a) PC mix, (b) FA mix, (c)

GGBS mix (Legend on Figure 4(b)) and (d) simulated response for PC mix at

10, 20, 30 and 40mm using equation (5) and fitting parameters in Table 3.

Figure 5 Schematic diagram of concrete (a) three-phase system comprising air, pore-

fluid and solids just prior the start of water-absorption, and (b) after 24-hour

water absorption test where the pore system is assumed to be fully saturated

and o/t has reached the steady-state condition (o/ss). In this Figure, Sr is the

degree of pore saturation before absorption, is the total porosity and eff the

effective porosity.

Figure 6 Water penetration depth versus square root of elapsed time for w/b = 0.6

concrete mixes (a) C1 cured and (b) C2 cured.

Figure 7 The cumulative water gain per unit area of inflow surface (mm3/mm2) versus

square root of elapsed time for C1 and C2 (a) w/b = 0.4 and (b) w/b = 0.6.

Figure 8 Showing how the depth of penetration and cumulative volumetric gain results

(FA concrete; w/b = 0.6 and C2 curing) can be used to evaluate the effective

porosity.

Figure 9 Conductivity profiles through the concrete samples before and after 1st and 2nd

water absorption cycles for the PC concrete mixes: (a) w/b = 0.4: C1 curing,

(b) w/b = 0.4: C2 curing, (c) w/b = 0.6: C1 curing, and (d) w/b = 0.6: C2

curing. (Legend on Figure 9(a))

Figure 10 Conductivity profiles through the concrete samples before and after 1st and 2nd

water absorption cycles for the FA concrete mixes: (a) w/b = 0.4: C1 curing,

(b) w/b = 0.4: C2 curing, (c) w/b = 0.6: C1 curing, and (d) w/b = 0.6: C2

curing. (Legend on Figure 10(a))

Figure 11 Conductivity profiles through the concrete samples before and after 1st and 2nd

water absorption cycles for the GGBS concrete mixes: (a) w/b = 0.4: C1

curing, (b) w/b = 0.4: C2 curing, (c) w/b = 0.6: C1 curing, and (d) w/b = 0.6:

C2 curing. (Legend on Figure 11(a))

Captions for Tables

Table 1 Oxide composition of cementitious materials

Table 2 Summary of concrete mixes (w/b = water-binder ratio, FA = fly ash, GGBS =

ground granulated blast-furnace slag). Figure in brackets is the standard deviation

for the compressive strength.

Table 3 Properties of Coarse and Fine Aggregates

Table 4 Modelling parameters for equation (5) (CoD = coefficient of determination for

fitting curve).

Table 5 Cumulative volumetric gain, i (mm3/mm2) after 24-hours absorption.

Table 6 Relative humidity before/after 1st absorption cycle for C1 and C2 curing.

Table 1 Oxide composition of cementitious materials

Oxide % SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O TiO2 SO3 LOI

CEM I 20.6 4.8 3.17 63.9 2.53 0.54 0.08 - 2.8 -

Fly Ash 48 29 9 2.5 3 3 1.3 0.9 0.7 3.3

GGBS 34 12.6 0.6 41 8.3 0.47 0.25 - - -

Table 2 Summary of concrete mixes (w/b = water-binder ratio, FA = fly ash, GGBS = ground granulated blast-furnace slag). Figure in brackets

is the standard deviation for the compressive strength.

Mix

Designation

w/b CEM

I

kg/m3

GGBS

kg/m3

FA

kg/m3

20mm

kg/m3

10mm

kg/m3

Fine

(<5mm)

kg/m3

Slump

(mm)

f28

MPa

f180

MPa

Plasticiser

l/m3

PC

0.40 370 - - 687 459 766 60 88.5

(0.95)

99.2

(1.44)

3.0

0.60 290 - - 687 458 765 50 43.4

(0.87)

54.7

(2.51)

0.5

FA35

0.40 240 - 130 672 448 744 65 51.4

(0.38)

80.0

(1.15)

3.5

0.60 188 - 102 674 450 748 50 25.6

(0.35)

40.8

(0.95)

0.6

GGBS65

0.40 130 240 - 681 454 757 65 45.6

(2.26)

66.7

(0.58)

2.5

0.60 102 188 - 682 455 758 50 30.1

(0.79)

47.7

(2.31)

0.6

32

Table 3 Properties of Coarse and Fine Aggregates

Aggregate

Type

Absorption

(%)

Bulk density

(loose)

(kg/m3)

Specific

gravity

Fineness

Modulus

AIV*

(%)

Coarse 1.02 1450 2.63 6.04 8.2

Fine 2 1520 2.63 2.89 +

*AIV: aggregate impact value

Table 4 Modelling parameters for equation (5) (CoD = coefficient of determination for

fitting curve).

Depth (mm) c g (hrs-1) tm (hrs) s CoD (r2)

10 1.22 1.57 0.46 0.08 0.97

20 0.74 0.60 3.17 0.26 0.99

30 0.61 0.24 9.07 0.40 0.99

40 0.56 0.28 10.8 0.45 0.99

Table 5 Cumulative volumetric gain, i (mm3/mm2) after 24-hours absorption.

Mix C1 C2

w/b = 0.4 w/b = 0.6 w/b = 0.4 w/b = 0.6

PC 1.01 1.30 1.46 2.02

GGBS/65 0.63 2.90 1.96 5.15

FA/35 0.74 1.77 0.97 4.01

33

Table 6 Relative humidity before/after 1st absorption cycle for C1 and C2 curing.

C1 Curing

Depth

(mm)

PC GGBS/65 FA/35

w/b = 0.4 w/b = 0.6 w/b = 0.4 w/b = 0.6 w/b = 0.4 w/b = 0.6

Before After Before After Before After Before After Before After Before After

25 88 100 87 100 88 100 87 100 89 100 89 100

50 87 96 87 100 90 100 87 100 90 100 89 100

100 88 88 87 87 90 90 88 92 89 89 90 94

175 87 87 87 89 90 90 90 91 89 89 90 90

C2 Curing

25 80 100 80 100 81 100 86 100 85 100 85 100

50 87 100 83 100 87 100 87 100 90 100 88 100

100 88 88 88 97 90 90 88 100 90 90 90 94

175 88 88 87 87 90 90 90 92 89 89 90 93

34

(a)

(b)

Figure 1

Thermistor

Curved inner surface of cavity lined with plastic sleeve

Thermistor

Sealed surface

Mastic seal

Electrode-pairs

Rubber

bung

RH sensor

35

Figure 2

15

20

25

30

35

40

45

0 10 20 30

Time (hrs)

Te

mp

era

ture

( C

)

36

Figure 3

Water reservoir

Test cell

Graduated

Burette.

Resistance

measurement

and multiplexing

system.

37

0

0.2

0.4

0.6

0.8

1.0

1.2

0 5 10 15 20 25

(a)

Time (hrs)

o /

t

0

0.2

0.4

0.6

0.8

1.0

1.2

0 5 10 15 20 25

10mm20mm30mm40mm50mm100mm175mm

(b)

Time (hrs)

o /

t

38

Figure 4

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15 20 25

(c)

Time (hrs)

o/

t

0

0.2

0.4

0.6

0.8

1.0

1.2

0 5 10 15 20 25

(d)

40mm

30mm

20mm

10mm

Time (hrs)

o /

t

39

Figure 5

(a)

Solids

s

Pore-water

Air

eff

Sr

Solids

s

Just prior to absorption:

Conductivity = o

After absorption:

Conductivity = ss

Pore-water

(b)

40

Figure 6

0

10

20

30

40

50

0 1 2 3 4 5

PC: d = 8.53t1/2

- 1.87 (r2 = 0.92)

FA: d = 10.8t1/2

- 0.143 (r2 = 0.98)

GGBS: d = 18.8t1/2

- 3.72 (r2 = 0.94)

(a) C1 curing

(Time, t)1/2

(hrs1/2

)

De

pth

, d

(m

m)

0

10

20

30

40

50

0 1 2 3 4 5

PC: d =9.61t1/2

+ 3.04 (r2 = 0.98)

FA: d = 26.5t1/2

- 3.59 (r2 = 0.98)

GGBS: d = 25.6t1/2

+ 0.876 (r2 = 0.96)

(b) C2 curing

(Time, t)1/2

(hrs)1/2

De

pth

, d

(m

m)

41

Figure 7

0

0.5

1.0

1.5

2.0

0 1 2 3

C1/PC: i = 0.166t1/2

+ 0.044 (r2 = 0.99)

C2/PC: i = 0.235t1/2

+ 0.093 (r2 = 0.98)

C1/FA: i = 0.106t1/2

+ 0.021 (r2 = 0.99)

C2/FA: i = 0.222t1/2

+ 0.023 (r2 = 0.99)

C1/BS: i = 0.082t1/2

+ 0.052 (r2 = 0.99)

C2/BS: i = 0.739t1/2

+ 0.163 (r2 = 0.94)

(a)

(Time, t)1/2

(hrs)1/2

i (

mm

3/m

m2)

0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3

C1/PC: i = 0.182t1/2

+ 0.022 (r2 = 0.99)

C2/PC: i = 0.533t1/2

- 0.016 (r2 = 0.99)

C1/FA: i = 0.661t1/2

- 0.103 (r2 = 1.0)

C2/FA: i = 1.09t1/2

+ 0.006 (r2 = 99)

C1/BS: i = 0.468t1/2

+ 0.11 (r2 = 0.99)

C2/BS: i = 1.03t1/2

+ 0.261 (r2 = 0.99)

(b)

(Time, t)1/2

(hrs)1/2

i (

mm

3/m

m2)

42

Figure 8

0

10

20

30

40

50

0 1 2 30

1

2

3

(Time, t)1/2

(hrs)1/2

Dep

th,

d

(mm

)

i (

mm

3/m

m2)

43

0

0.5

1.0

1.5

0 50 100 150 200

Before: 1st Cycle

After: 1st Cycle

Before: 2nd

Cycle

After: 2nd

Cycle

(a) w/b = 0.4: C1

Depth (mm)

( 1

0-4

S/c

m)

0

0.5

1.0

1.5

0 50 100 150 200

(b) w/b = 0.4: C2

Depth (mm)

( 1

0-4

S/c

m)

44

Figure 9

0

0.5

1.0

1.5

0 50 100 150 200

(c) w/b = 0.4: C2

Depth (mm)

( 1

0-4

S/c

m)

0

1

2

3

0 50 100 150 200

(d) w/b = 0.6: C2

Depth (mm)

( 1

0-4

S/c

m)

45

0

0.5

1.0

1.5

2.0

0 50 100 150 200

Before: 1st

Cycle

After: 1st Cycle

Before: 2nd

Cycle

After: 2nd

Cycle

(a) w/b = 0.4: C1

Depth (mm)

( 1

0-4

S

/cm

)

0

0.5

1.0

1.5

2.0

0 50 100 150 200

(b) w/b = 0.4: C2

Depth (mm)

( 1

0-4

S/c

m)

46

Figure 10

0

0.5

1.0

1.5

2.0

0 50 100 150 200

(c) w/b = 0.6: C1

Depth (mm)

( 1

0-4

S

/cm

)

0

0.5

1.0

1.5

2.0

0 50 100 150 200

(d) w/b = 0.6: C2

Depth (mm)

( 1

0-4

S/c

m)

47

0

0.5

1.0

1.5

0 50 100 150 200

Before: 1st Cycle

After: 1st Cycle

Before: 2nd

Cycle

After: 2nd

Cycle

(a) w/b = 0.4: C1

Depth (mm)

( 1

0-4

S

/cm

)

0

0.5

1.0

1.5

0 50 100 150 200

(b) w/b = 0.4: C2

Depth (mm)

( 1

0-4

S/c

m)

48

Figure 11

0

1

2

3

0 50 100 150 200

(c) w/b = 0.6: C1

Depth (mm)

( 1

0-4

S

/cm

)

0

0.5

1.0

1.5

0 50 100 150 200

(d) w/b = 0.6: C2

Depth (mm)

( 1

0-4

S/c

m)