The Influences Of Chemical Admixtures On The Performances Of Sulfoaluminate Expansive Agents

The expansive agents are widely applied in shrinkage-compensating concrete and self-stressing concrete. In practice, expansive agents are usually used by combining with other chemical admixtures. These other admixtures mainly include superplasticizers and retarders, or compound admixtures with ingredients of superplasticizers and retarders. The researches into the influences of superplasticizers and retarders on the efficiency of expansive agent have been seldom reported at present. Under not knowing about the combining effects of expansive agents with other chemical agents, people often blindly design, select and expand the scope of application, so resulting in many concrete projects added with expansive agents not to achieve the designed effects.Therefore, in this paper, the influences of superplasticizers, retarders and compound admixtures with ingredients of superplasticizers and retarders on the efficiency of sulfoaluminate expansive agent were systemicly investigated.The influences of three superplasticizers, three retarders and compound admixtures with ingredients of superplasticizers and retarders on the performances of expansive agent were studied, which include the free expansion rate, restrained expansion rate, expansion index and the compressive strength. The laws of these chemical admixtures affecting the expansive performance and compressive strength of expansive agent were also concluded. Compared with standard mortar specimens added with expansive agent separately, the mortar specimens added with expansive agent and other chemical admixtures had the following different performances:(1) The free expansion rate and restrained expansion rate of specimens with superplasticizers and expansive agents decrease obviously in water curing conditions. The free expansion rate and restrained expansion rate of specimens with polycarboxylic acid series superplasticizer decrease mostly. In air curing condition, the early free expansion rate and restrained expansion rate decrease. The specimens shrinkage during 14d-28d, and their shrinkage rates are higher than that of the standard mortar specimens. The shrinkage rates of specimens with naphthalene series superplasticizer increase mostly.(2) The compounding use of expansive agent and sodium tripolyhosphate or sodium gluconate retarders can increase the free expansion rate, but decrease the restrained expansion rate of expansive agent in water or standard curing condition. However, both the free expansion rate and restrained expansion rate of specimens with calcium sugar retarders decrease in water or standard curing condition.(3) The free expansion rate and restrained expansion rate of specimens with expansive agent, superplasticizers and retarders decrease in water curing condition, especially the early expansion rates decrease evidently. In air curing condition, the free expansion rate and restrained expansion rate decrease during 7d-14d. The specimens shrinkage during 14d-28d, and their shrinkage rates are higher than that of the standard mortar specimens.(4) when expansive agent is compounded with these chemical admixtures, the expansion indexes of mortar specimens at 28d in water curing condition increase, and the compressive strengthes at experimental age under the same fluidity increase obviously.In summary, if compounding expansive agents with superplasticizers and retarders, the effect of expansive agents can decrease. Therefore, it is necessary that experiment should be carried out to confirm the effect of expansive agents in engineering application.