Study On The High-Strength Concrete Early-Age Cracking Regularity

With the development of concrete technology, high-strength concrete has been widely used in engineering, its good performance brought huge economic benefits to the society. But the engineering practice shows that high strength concrete are more likely to have early cracking phenomenon, and the existence of cracks will not only influence the appearance, will cause serious influence to concrete durability. Thus, there is an actual significance to pay attention to the study on high-strength concrete early cracking.In order to study the influence of preparation factor, unitary and compound mineral admixture and different replacement percentages of desert sand on the early-age plastic shrinkage crack of concrete, this paper adopted the constraints around the plate method. Meanwhile, the early-age plastic shrinkage crack mechanisms of concrete were analyzed. The experimental results showed that:(1) When w/b was in the range of 0.34 to 0.40, with the increase of w/b, the evaporation rate of 24h increased and early cracking tendency were also gradually increase; To a certainty of sand percentage (38%-44%), with the increase of sand percentage, the evaporation rate of 24h decreased, then early cracking degree increased, anti-crack performance worse and worse.(2) In terms of single mineral admixtures mixing, the incorporation of fly ash and slag on the early-age concrete plastic cracking are good inhibitory effect; Silicon fume could increase the early-age plastic cracking of concrete, and with the increase of dosage of cracking are becoming ever more obvious. In aspects of mineral admixture mixed, fly ash, slag, silica fume binary blends could improve 28d compressive strength of concrete, but the effect is not significant; On early cracking of concrete, mineral admixture mixed were significantly enhance the crack resistance of concrete, has played a good composite effect.(3) With the increase of sand to common medium sand desert, the 28d compressive strength is the trend of first increases and then decreases.In terms of early cracking test, when the desert sand for medium sand replacement ratio is less than 40%, the concrete early crack resistance decreased with the increase in replacement percentages; When the desert sand for medium sand replace rate is more than 40%, the crack resistance of concrete increase with the increase in replacement percentages, among them, when replacement ratio was 80% and 100%, the cracking area of concrete was reduced by 15.5% and 37.7% respectively compare with ordinary concrete.