Effect Mechanism Research Of Water Reducers On Dry Shrinkage Of Cement Concrete

The shrinkage-crack quality is one of the most important factors which have great influences on durability of cement concrete. Modern concrete characterized by high-efficiency water reducers and mineral additions failed to improve its shrinkage quality while met the demands of workability and strength. A great deal of researches have been carried out on this problem, however, no answers of perfection have been put forward to. Therefore, researches of deeper level on the shrinkage quality of cement concrete are urgently required.This paper have carried out researches around the influences of high efficiency water reducers on dry shrinkage quality of cement concrete from both micro mechanism and macro performance:Firstly, by immigrating knowledge of surface physical chemistry we designed an effective method using for measuring the contact angle which can present the adsorptive capacity between intern pore surface of hardened cement paste and water; secondly, based on cement paste, we changed the mixing factors such as W/C ratio, varieties and mixing quantities of water reducers, varieties and mixing quantities of mineral additions etc to carried out systematical researches on dry shrinkage quality of cement paste, furthermore, probe into the dry shrinkage mechanism and try to find out the working factors which influence the quality most; thirdly, systematical studies on dry shrinkage quality of concrete with different mixing match were also done through two aspects named as free shrinkage and restrict shrinkage to seek after the influences of water reducers and mineral additions on shrinkage quality of concrete under different restrict conditions; fourthly, we did some primary discuss on restraining methods for improving shrinkage quality of high performance concrete, two effective solutions were found.Through the work above we found that the contact angle testing meathod in this paper is obviously effective in presenting the hydrophilic nature of intern pore surface of hardened cement paste, analysis based on this method can be integrated with shrinkage testing results very well.Through a series of cement paste experiments several conclusions came out: the mixing of water reducers have greatly changed the hydrophilic nature of intern pore surface of hardened cement paste, thus changed the shrinkage pressure when paste loses water in dry conditions, so as to the dry shrinkage quality of cement paste, to sum up, the changes of contact angle between pore surface and water is one of the most important influences on dry shrinkage quality of cement paste; different kinds of water reducers and mineral additions have different influences on dry shrinkage quality.Concrete experiments show that water reducers have greater influence on concrete with lower W/C ratio than that of higher ones, and the effect became even more evident when concrete was in restrict conditions; multi-component compound concrete with double mixing expansive agents and mineral additions have good shrinkage restraining and crack preventing capacity, shrinkage reducing agent can be used together with expansive agent to doubly reducing concrete shrinkage.