Abstract

As water is becoming a scarce material day-by-day, there is an urgent need to do research work pertaining to saving of water in making concrete and in constructions. Curing of concrete is maintaining satisfactory moisture content in concrete during its early stages in order to develop the desired properties. However, good curing is not always practical in many cases. Curing of concrete plays a major role in developing the concrete microstructure and pore structure and hence improves its durability and performance. Keeping importance to this, an attempt has been made to develop self curing concrete by using water-soluble Polyethylene Glycol as self-curing agent and light weight aggregate as Granite.

The aim of this investigation is to study the strength and durability properties of concrete using water-soluble Polyethylene Glycol as self-curing agent. The function of self-curing agent is to reduce the water evaporation from concrete, and hence they increase the water retention capacity of concrete compared to the conventionally cured concrete. The use of self-curing admixtures is very important from the point of view that saving of water is a necessity everyday (each one cubic metre of concrete requires 3m3 of water in a construction, most of which is used for curing). In this study, compressive strength and split tensile strength of concrete containing self-curing agent is investigated and compared with those of conventionally cured concrete. It is found through this experimental study that concrete cast with Polyethylene Glycol as self-curing agent is stronger than that obtained by sprinkler curing as well as by immersion curing.

In the present study, the affect of admixture (PEG 400) on compressive strength, split tensile strength and modulus of rupture by varying the percentage of PEG by weight of cement from 0% to 2% were studied for M20. It was found that PEG 400 could help in self curing by giving strength on par with conventional curing. It was also found that 1% of PEG 4000 by weight of cement was optimum for M20 grade concretes for achieving maximum strength without compromising workability.

INTRODUCTION

Fresh concrete or plastic concrete is a freshly mixed material which can be moulded into any shape. The relative quantities of Cement ,aggregates and water mixed together , control the properties of concrete in wet state as well as in the hardened state.

Curing of concrete is maintaining satisfactory moisture content in concrete during its early stages in order to develop the desired properties and therefore it is one of the most important requirements for optimum concrete performance in any environment or applications. However, good curing is not always practical in many cases. Therefore, the method of using self-curing agents will be a good alternative.

Self Curing

The ACI-308 code states that “Internal curing refers to the process by which the hydration of cement occurs because of the availability of additional internal water that is not part of the mixing water.” “Internal curing” is often also referred as Self–curing. Self Curing Concrete can be achieved by adding self curing agents. The concept of self-curing agents is to reduce the water evaporation from concrete and hence increase the water retention capacity of the concrete. It was found that water soluble polymers can be used as self-curing agents in concrete. Curing of concrete plays a major role in developing the concrete microstructure and pore structure and hence improves its durability and performance.

A. Methods of Self- Curing (Internal Curing):

Currently, there are two major methods available for internal curing of concrete. The first method uses saturated porous lightweight aggregate (LWA) in order to supply an internal source of water, which can replace the water consumed by chemical shrinkage during cement hydration. The second method uses poly-ethylene glycol (PEG) which reduces the evaporation of water from the surface of concrete and also helps in water retention.

POLYETHYLENE GLYCOL

Polyethylene glycol is a condensation polymer of ethylene oxide and water with the general formula H(OCH2CH2)nOH, where n is the average number of repeating oxyethylene groups typically from 4 to about 180. The abbreviation (PEG) is termed in combination with a numeric suffix which indicates the average molecular weights. One common feature of PEG appears to be the water-soluble nature. Polyethylene glycol is non-toxic, odorless, neutral, lubricating, non-volatile and non-irritating and is used in a variety of pharmaceuticals.

CHEMICAL PROPERTIES OF PEG (POLYETHYLENE GLYCOL)

PEG 400 is strongly hydrophilic. The partition coefficient of PEG 400 between hexane and water is 0.000015 (log P = -4.8), indicating that when PEG 400 is mixed with water and hexane, there are only 15 parts of PEG 400 in the hexane layer per 1 million parts of PEG 400 in the water layer. PEG 400 is soluble in water, acetone, alcohols, benzene, glycerine, glycols, and aromatic hydrocarbons, and is slightly soluble in aliphatic hydrocarbons

PHYSICAL PROPERTIES OF PEG (POLYETHYLENE GLYCOL)

Depend on molecular weight the wide range of the physical property such as solubility, hygroscopic, vapour pressure, melting or freezing point and viscosity are variable: Solubility- Increasing the molecular weight of PEG results in decreasing solubility in water & solvents. PEG are also soluble in many polar organic solvents such as acetone, alcohols. Hygroscopic- PEGs are hygroscopic, it means that they attract and retain moisture from the atmosphere. Hygroscopic decrease as molecular weight increases. Viscosity- PEGs can be considered Newtonian fluids, so the kinematic viscosity of PEGs decreases as temperature increases. Stability- PEGs have low volatility and are thermally stable for a limited period of time below 300°c and without O2

METHODS OF SELF-CURINGBy using saturated porous lightweight aggregate

(LWA) to supply internal soure of water for hydration of cement

By using poly-ethylene glycol (PEG) to retain water in concrete by reducing evaporation of

water from the surface

LIGHT WEIGHT AGGREGATES

Wen-Chen Jau stated that self curing concrete is provided to absorb water from moisture

from air to achieve better hydration of cement in concrete. It solves the problem when the

degree of cement hydration is lowered due to no curing or improper curing by using a selfcuring

agent like poly-acrylic acid which has strong capability of absorbing moisture from

the atmosphere and providing water required for curing concrete.

M.V.Jagannadha Kumar, M.Srikanth, Dr.K.Jagannadha Rao studied that the optimum dosage

of PEG400 for maximum strengths (compressive, tensile and modulus of rupture) was found

to be 1% for M20 and 0.5% for M40 grades of concrete. As percentage of PEG400 increased

slump increased for both M20 and M40 grades of concrete. Strength of self-curing concrete is

on par with conventional concrete. Self-curing concrete is the answer to many problems faced

due to lack of proper curing.

A.Aielstein Rozario, Dr.C.Freeda Christy, M.Hannah Angelin said that the permeability of

concrete decreases with an increase in the replacement of fly ash with cement and in addition

of P.E.G dosages. So the penetration of chemicals is decreased with the addition of PEG and

the concrete is safe against sulphates. The percentage of weight loss of the concrete

specimens are also decreased for every grades of concrete. From the results, we know that the

self- curing concrete has the ability to resist the sulphates present in the soils and in the sea

waters. It is very economical also, so it can be adoptable for the constructions.

PietroLura The main aim of his study was to reach a better comprehension of autogenous

shrinkage in order to be able to model it and possibly reduce it. Once the important role of

self-desiccation shrinkage in autogenous shrinkage is shown, the benefits of avoiding selfdesiccation

through internal curing become apparent.

Ole and Hansen describe a new concept for the prevention of self-desiccation in hardening

cement-based materials using fine, super absorbent polymer (SAP) particles as a concrete

admixture. The SAP will absorb water and form macro inclusions and this leads to water

entertainment, i.e. the formation of water-filled macro pore inclusions in the fresh concrete.

Consequently, the pore structure is actively designed to control self-desiccation. In this work,

self-desiccation and water entertainment are described and discussed.

Roland Tak Yong Liang, Robert Keith Sun carried work on internal curing composition of

concrete which includes a glycol and a wax. The invention provides for the first time an

internal curing composition which, when added to concrete or other cementations mixes

meets the required standards of curing as per Australian Standard AS 3799.

A.S. El-Dieb investigated water retention of concrete using water-soluble polymeric glycol as

self-curing agent. Concrete weight loss and internal relative humidity measurements with

time were carried out, in order to evaluate the water retention of self-curing concrete. Water

transport through concrete is evaluated by measuring absorption%, permeable voids%, and

water sorptivity and water permeability. The water transport through self-curing concrete is

evaluated with age. The effect of the concrete mix proportions on the performance of selfcuring

concrete was investigated, such as, cement content and water/cement ratio.