Experiment Study On The Concrete Early-age Shrinkage And Anticrack Properity

During the technology development of modem concrete, concrete structure crack (especially early-age crack) becomes more and more serious and has been one of main research directions of civil engineering. This paper aims at the seriousness of concrete structure crack and presents one of main cause is that concrete early-age (especially autogenous shrinkage)become large through the systems academic analysis. By the apparatus for measuring early-age shrinkage, the principle of this shrinkage and the measures to control it has been studied in this paper.A new type of apparatus for measuring early-age shrinkage is presented on the basis of advantages and disadvantages of the fellow apparatus in or abroad. Sufficient tests indicate manifestly the apparatus has the characters of high accuracy,good paleognesis and convenience.The paper has studied the influence of water-cement ratio on the early-age shrinkge and whole shrinkge through self-deviced experimental apparatus for measuring early-age shrinkage. The result of test shows it is not accurate to estimate concrete shrinkage if the early-age shrinkge is ignored, since theearly-age shrinkge comprises the most part of the whole shrinkge. Simultanously, the influence of mineral admixture on the early-age shrinkge and early-age shrinkage mechanisms is studied in this paper.Due to the fact that the study consequence about the influence of water-reducing admixture on the early-age shrinkge is scarce, this paper also broadly study influence of water-reducing admixture on the early-age shrinkge,drying shrinkage and whole shrinkge. The tests results show three types of water-reducing admixture all increase concrete early-age shrinkage by 200%-300% and whole shrinkage by 80%-90%,beyond the amplitude of specification at present.Adding expansive admixture is the main material measures to control concrete structure crack in our country at present, However, influence of expansive admixture on the early-age shrinkge has never been reported detailedly in or abroad. This part is investigated in this paper. What's more, a new type admixtures-shrinkage-reducing admixture is also studied with respct to theconcrete shrinkage. Results indicates that expansive admixture and shrinkage-reducing admixture both decrease early-age shrinkage,but the shrinkage-reducing admixture has the merits of more stable shrinkage-reducing ratio ,lower drop in elavation of shrinkage , more substantial reduction in overall shrinkage and so on. Therefore, shrinkage-reducing admixture is a new type of admixture that is worthy of researching and popularizing.The ring test result shows that tendency of concrete cracking is consistent with shrinkage and veritifies early-age shrinkage is responsible for the concrete early-age crack.