Research On The Application Of Polycarboxylate Superplasticizer In Ready-Mixed Concrete

Nowadays, polycarboxylate superplasticizer (PC) has been widely used in high performance concrete in China, but it is hardly used in the ready-mixed concrete industry. Most researchers have paid their attentions on how to prepare high performance concrete with PC. It should be noted that there is little effect have been made to investigate its use in plain ready-mixed concrete, and there is no paper published on this subject. Thus, the research on the application of PC in the ready-mixed concrete is systematically studied in this thesis.The factors (i.e., raw materials, common used admixtures and mix proportions) that influence the application of PC in ready-mixed concrete were experimentally studied. It showed that its performance was sensitively influenced by the factors such as properties of cement and fly ash, poor compatibilities with the commonly used water-reducers and expanding agents, sand ratio and mix proportion. These problems have become the main factors that seriously limit the use of PC in ready-mixed concrete.By comparing the properties of ready-mixed concretes containing PC and naphthalene water reducer, it showed that mix with PC had a higher slump, as well as a reduction of slump loss of 15～20%. At the same time, an 10%-improvement of strength and 10%~20%-reduction of shrinkage can be obtained. Based on the main factors that influence the plasticizing effects of PC, the change law of PC concrete mix design was studied by orthogonal design with naphthalene-based mix design as the reference. The change law is shown as following: a reduction of binder to 3% degree ( a reduction of cement to 6% degree, an enhancement of mineral mixtures to 8%), an improvement of sand ratio to 0.5% and a reduction of water to 6% degree.Then, the practical problems of using PC in ready-mixed concrete industry (the corrosion risks of PC containers and pipes, the great immediate loss of mix workability and bleeding of the second addition of PC, etc.) were analyzed and solved. The problems of the corrosion of PC containers and pipes can be solved by adjust the PC solution to a weak alkaline environment (pH=7.5); the problem of the great immediate loss of mix workability due to the high loss of ignition of fly ash can be solved by adding air entraining agent to a certain degree; the problem of bleeding of the mix after the second addition of PC can be solved by introduction of lignosulphonate. Finally, the self-compacting plain concretes of the low(C30), high(C50) grades and the high strength concrete (C80) were prepared according to the development routine of high-valued ready-mixed concrete by using the local materials of Chongqing, and they were successfully used in practice.