The Effect of Water to Cement Ratio on Early Age Properties ......Early Age Monitoring of Cement Paste using Ultrasonic Test Figure 1 Schematic representation of typical evolution

The Effect of Water to Cement Ratio on Early

Age Properties of Cement Paste and Mortar by

UPV

Mohit Gupta Dept. of Civil Engineering

BRCM College Bahal,

Haryana (INDIA)

Dr. Arabinda Sharma Dept. of Civil Engineering

Associate Professor,

BRCM College Bahal,

Haryana (INDIA)

Abstract - The research work done through an experimental

investigation carried out to study the effect water to cement

ratio on early age properties of cement paste and mortar are

investigated using an ultrasonic pulse velocity method.

Properties that are difficult to determine to the early age

performance of these are tested, including setting and

hardening time, strength development and compressional

wave (P-wave) arrival. Measurements of these properties

using an ordinary Portland cement (OPC) are presented for

cement paste having water to cement ratio 0.40 and 0.45.

These properties were also measured for mortar having water

to cement ratios (0.40, 0.45 and 0.50). Early age setting time

behaviours of cement pastes and mortar are contrasted. It

was found that while increasing the water to cement ratio

ultrasonic pulse velocity decreases at early age.

Key words: Ultrasonic Monitoring, Setting,Strength

Development, Prolonged Agitation

INTRODUCTION:

The development of microstructure in a cementitious

material matrix evolves occurs during the setting process

due to the ongoing hydration occurring in the cement paste

and mortar. When cement paste and mortar transforms

from suspension to solid mode the strength parameters

change with time. The evolution of microstructure as a

result of hydration reduces the porosity and increases the

strength. This change is relatively rapid during the first day

of hydration and slows down over time.

The ultrasonic method can be used to follow setting. The

change of ultrasonic velocity over time is sensitive to the

differences in setting behaviour of the tested mixtures.

Initial setting seems to correspond with the point of

inflection of the velocity-vs.-time graph and final setting

time with point at which the velocity becomes constant.

Methodology:

Continuous monitoring of setting and hardening

process was performed using two cement paste

mixtures of water to cement ratios (w/c=0.40 and

w/c =0.45) and three mortar mixtures of water to

cement ratios (w/c=0.40, w/c=0.45 and w/c=0.50).

Also effect of sand to cement ratios (s/c=0.25,

s/c=0.50 and s/c=3) on setting and hardening in

mortar keeping water to cement ratio constant

(w/c=0.50) was studied.

LITERATURE REVIEW:

United States researcher Dr. Floyd Firestone first applied

this method in 1940. After two years the applicability of

the instrument used for the method was validated and it

was titled as ‘Flow detecting device and measuring

instrument’. The device was then used by many researchers

for measuring the presence of inhomogeneity in density

and elasticity of concrete materials.

James F. McNulty (1966) performed this test on using

piezoelectric transducers and named it as ‘Ultrasonic

testing apparatus and Method’. According to him, the

crystals vibrates at ultrasonic frequencies and the wave is

transmitted to the object being studied through a

mechanical coupling.

Reinhardt (2004) developed test setup for the exact

determination of transmitted ultrasonic pulse. It was shown

that the good estimate of initial setting time can be

determined from the velocity vs. age of cement paste by

mathematical procedure and final setting time can be

determines using empirical experience relationships.

Vol. 5 Issue 05, May-2016

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181http://www.ijert.org

IJERTV5IS050698

(This work is licensed under a Creative Commons Attribution 4.0 International License.)

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Early Age Monitoring of Cement Paste using Ultrasonic Test

Figure 1 Schematic representation of typical evolution of UPV in cement pastes.

Source: (Lee et al., 2004)

The development of the microstructure properties of

cement based materials at early age can be measured using

ultrasonic technique. Lange (1994) said that electron

microscopy image can also be used to analyse the

microstructure. Sayer et al. (1993) have captured that for

cement paste, the ultrasonic pulse velocity is significant in

the suspension phase after mixing until the time of

complete hydration where particles are interconnected.

This observation holds importance in the determination of

early age properties Boumiz, et al. (1996) performed

experimental correlation tests measuring UPV, heat flow

and electrical conductivity.

EXPERIMENTAL PROGRAM

The experimental investigations involve monitoring of

the compressional wave velocity in a cement paste and

mortar sample for an extended duration in order to

understand the effect of continuous agitation on the

velocity. The objective is to correlate the evolution of the

velocity to the gain or loss of strength of the sample

under continuous agitation condition which is prevalent

in ready mix concrete supply vehicles.

Table 1: Overview of the test matrix for Continuous monitoring of UPV

Table 1 shows the various w/c ratios and sand to cement

ratios used to prepare the various cement paste and

mortar samples. The evolution of the compressional

wave velocity of the various mortar samples as a

function of time and the duration of agitation is

investigated.

Measuring compressive strength of cement mortar for

various agitation durations. Also, UPV is measured for

certain durations of agitation such as 60 minute, 120

minute, 180 minute, 240 minute we have also measured

UPV for the non-agitated sample. On day one, we cast 3

cubes each for agitation duration of 30 minute, 60

minute, 90 minute, and so on till 360 minute for

measuring 7 days compressive strength. Similarly, on

day two we cast 3 cubes each for the same agitation

durations for measuring 28 days compressive strength.

MATERIALS

1.Cement

Single type of cement (OPC 43 Grade) was used in this

project. Adequate quantity of cement was purchased taking

wastage into consideration. Various properties of the

cement used in preparation of the samples are enumerated

in Table 2

Cement paste w/c=0.40 w/c=0.45 -

Mortar (various w/c ratio) w/c=0.40, s/c=3 w/c=0.45, s/c=3 w/c=0.50, s/c=3

Mortar (various s/c ratio) w/c=0.50, s/c=0.25 w/c=0.50, s/c=0.25 w/c=0.50, s/c=0.25




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Table 2: Physical Characteristics of cement

Parameter Measured Portland Cement

Type of cement Ordinary Portland

Grade OPC 43

Standard Consistency 31.5 %

Initial/Final setting time (minute) 103/365

Specific gravity of cement (gm/ml) 3.15

2.Fine aggregate

The sieve analysis of the sand was performed according to the procedure given in IS 2386: Part -1 (Table-2). Sand of about

2000gm weight was taken for final sieving.

SIEVE ANALYSIS FOR SAND

Size Of Weight Percentage Cumulative Percentage Limit

Sieve Retained on Weight Percentage Passing (mm) Sieve (gm) Retained Weight

Retained

10 0.00 0.00 0.00 100.00 100

4.75 108 5.41 5.41 94.59 90-100

2.36 131.8 6.59 12.00 5.41 75-100

1.18 258.7 12.94 24.94 12.00 55-90

0.60 441.3 22.06 47.00 24.94 35-59

0.30 708.5 35.43 82.43 47.00 8-30

0.15 191.5 9.57 92.00 82.43 0-10

Pan 160 8.00 100 92.00 -

Total 2000 100 - 100

3.Water

Normal potable water from the laboratory was used.

Preparation of Samples for the UPV Test

1 Cement paste

Cement and water were mixed initially with the mixer

being rotated at 140 rpm for 30s. The mixer was stopped

after 1 minute and then the mixing was resumed at 285 rpm

for 2 min 30s. The cement paste adhering to the sides of

mixer was scraped and mixed for another 2 min 30s

following the 1 min break. Cement pastes with w/c ratio

(w/c=0.40, w/c=0.45) were prepared with this technique.

2 Mortar

The mortar was mixed initially at 140 rpm for 1 min and

subsequently at 285 rpm for 2 min after the 1 minute pause.

The water to cement ratio was set at two values (w/c=0.40,

w/c=0.45, w/c=0.50), keeping the sand to cement ratio

constant. The same procedure was followed for three

different mixes with water to cement ratio kept constant at

0.50 and sand to cement ratio kept at 0.25, 0.50, and 3.




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Mix Design

The mix design for cement paste and cement mortar used in the experiments are shown in tabular form as follows:-

Table 3: Cement Paste Mixture proportions used in this study

Mix Water (litre) Cement (Kg)

Cement Paste (w/c= 0.40) 0.557 1.393

Cement Paste (w/c =0.45) 0 .586 1.302

Table 3 shows cement paste mixture prepared for the two different water-cement ratios and also the absolute quantities of

cement and water are shown.

ULTRASONIC TEST SETUP

Setup consists of a U-shaped foam rubber container and

two pieces of cover plates made of Plexiglas with thickness

of 8mm. The Plexiglas plates were held together by four

screws. Circular grooves were cut on both of the plates to

accommodate the ultrasonic transducers with center

frequency of 250 kHz. Grease was used as a couplant for

the transducers. The leakage of water though the sample is

prevented by properly tightening the screws between the

plates. A pulse is generated on one side of the specimen

and the arrival of the pulse is picked by the transducer on

the other side. The transmitted pulse are recorded and

digitized and averaged in an oscilloscope. After the test, the

plates and the mould are cleaned for future use.

Test Setup for UPV Measurement Test

RESULTS AND DISCUSSION-

RESULT OBTAINED FROM THE EXPERIMENTAL

INVESTIGATION IS

Variation of the slope of UPV versus Time UPV values were recorded at every 3 minutes interval. The

difference in the values of UPV after 60 minutes for every

3 min interval was calculated. This value was divided by

the duration which is 60 min at which the differences in the

value were calculated and this final value is the slope. And

this

graph shows the value of this slope at every 3 min

interval for two different cement paste mixtures with w/c

ratio of 0.40 and 0.45.




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Fig 2 shows that the ultrasonic pulse velocity is 201 m/s at approximately 35 min in cement paste having water to cement ratio

0.40. A comparable compressional wave velocity value of 230 m/s is reached approximately after an interval of 90 min for the

cement paste having w/c ratio of 0.45. Thus there is a delay in the compressional wave arrival with higher w/c ratio which is

consistent with later age strength development in cement pastes with higher w/c ratios

Fig 2 Influence of w/c ratio on Evolution of UPV with various w/c ratio

5

4.5

4

3.5

3

2.5

2

1.5

1

0.5

0

0 50 100 150 200 250 300 350 400 450

slope 0.4 TIME (MIN)

SLOPE 0.45

Fig 1 shows that the rate of strength development is higher in the paste having lower w/c ratio.




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Figure 3: Influence of s/c ratio on Evolution of UPV with Constant w/c ratio.

In the Fig 3 it can be seen that after six hrs, the value of

ultrasonic pulse velocity for cement mortar with s/c atio

0.25 is 1275 m/s, with s/c ratio 0.50 is 1000 m/s and with

s/c ratio 3 is 500 m/s. Thus it is observed that the ment

mortar with low s/c ratio have higher ultrasonic pulse

velocity as compared to cement mortar with high s/c ratio

at any particular period of time.

Comparison of UPV during Setting of Early Age Cement

Paste and Mortar

In this section, comparison is made between the cement

paste and the mortar having same w/c ratio. The first

appearance of the compressional wave for both the cement

paste and mortar is observed. And the ultrasonic pulse

velocity after 6 hrs. is measured for the cement paste and

mortar.

There is difference in the first appearance of the

compressional wave during early age for the cement paste

and the mortar. The first appearance of the compressional

wave in the cement paste is earlier than that in the mortar.

The first appearance of the compressional wave for cement

paste is after 30 minutes and for mortar after 125 minutes.

This can be explained by the fact that the rate of hydration is higher in cement paste as compared to the mortar.

CONCLUSION

An ultrasonic monitoring technique has been used

successfully to measure the Setting process of both

cement paste and mortar at early age. This technique

gives the clear picture of strength development. It could

be used on site without disturbing the concrete to check

strength development at early stage.

Sand to cement content decreases, the velocity of the

compressional wave’s increases. Hence, it may be

concluded that sand attenuation at early age is very high

through transmission measurements. Hence the ultrasonic

waves are influenced by the attenuation of sand. As the

sand content is decreased, the attenuation decreases and

ultrasonic

pulse velocity increases.

Water to cement ratio increases, the velocity of the

compressional waves reduces as the travel time of waves

is increases in the mixture. Hence the increases water

cement ratio the ultrasonic pulse velocity decreases.

Mortar:effect of constant w/c ratio and increasing s/c ratio

(m/s)

1400

Velocity

1200

Pulse 1000

Ultrasonic

800

600

400

200

0

0 50 100 150 200 250 300 350 400

Time (min.)

sand to cement ratio

0.25 sand to cement

ratio 0.5 sand to

cement ratio 3




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The Effect of Water to Cement Ratio on Early Age Properties ......Early Age Monitoring of Cement Paste using Ultrasonic Test Figure 1 Schematic representation of typical evolution