The Shrinkage And Cracking Of The Lightweight Aggregate Concrete With The Influence Of Nano-SiO₂

The shrinkage and cracking of concrete structure is one of the important factors affecting the durability of concrete. Lightweight aggregate concrete is the most widely used of concrete except of the normal concrete,and it's a new type of concrete.Compared with the normal concrete, it has light weight, high strength, thermal insulation, fire earthquake, good crack resistance and other excellent properties, and widely used in industrial and civil buildings and other industrial sectors.The mineral fine admixturewith with Nano-SiO2 has good filling effect, active effect and micro aggregate effect, applied to the concrete, can improve the early strength, and can also improve its internal microstructure.With the development and the demand of the society, "the high strength, light weight," has become the development trend of concrete.Although crack resistance of lightweight aggregate concrete is very good, but its intensity is low.And common concrete crack resistance is poorer, but its strength is higher.And nano-SiO2 also has good filling effect,active effect, and many other advantages, so the light weight aggregate concrete and ordinary concrete, and the principle of nano silica mineral fine admixture, has important research significance.This paper studies two kinds of ceramsite as the research object, designed two kinds of ceramsite replacement ratio, and at the same time adding nano silicon dioxide, a total of 24 group of mixture ratio design, to explore the long-term free of ceramsite and ordinary concrete plastic cracking and early shrinkage, and also discusses the ceramsite and nano silica on the mechanical properties such as compressive strength of concrete, the influence of the main results were as follows:(1) Through the 24 groups of age(a total of 72 test specimen) for 3 day, 7 day and 28 day cube compressive strength test available: ceramsite high strength on the strength of concrete cylinder pressure, the 28 d cube compressive strength of concrete along with the increase of ceramsite is on the decline.Within a certain range, with the increase of nano silicon dioxide content, the concrete compressive strength is also increased.Through the concrete microstructure of cement stone, explain the mechanism of nano silicon dioxide impactstrength.(2) through the 24 set of mixture ratio(a total of 72 specimens) experiment in long-term contract freely available: for lightweight aggregate concrete, high moisture content of ceramsite concrete preparation by early shrinkage is less than the low moisture content of the ceramsite concrete, but the late shrinkage is higher than the low moisture content of the ceramsite concrete.For mixing concrete, to nantong ceramsite, early shrinkage when the dosage was 50% less than ordinary concrete, the late than ordinary concrete contraction, and low moisture content yichang ceramsite.(2)Group of 24 mix(a total of 72 test specimen) experiment in long-term contract freely available: for lightweight aggregate concrete, high moisture content of ceramsite concrete preparation by early shrinkage is less than the low moisture content of the ceramsite concrete,but the late shrinkage is higher than the low moisture content of the ceramsite concrete.For mixing concrete, to nantong ceramsite, early shrinkage when the dosage was 50% less than ordinary concrete, the late than ordinary concrete contraction, and low moisture content yichang ceramsite, any content, early and late shrinkage were greater than normal concrete.Refine the long-term contract freely about unilateral ceramsite concrete moisture content model, the model and the theoretical results fit well with the experimental data, and the model can more accurately to 28 d experimental value to predict long-term contraction value.(3) Through the 24 groups of mixture ratio(a total of 48 pieces of tablet) plate cracking experiments available: for the moisture content of different ceramsite, cracking resistance of high moisture content of nantong ceramsite ceramsite significantly higher than that of low moisture content of yichang.For the same ceramsite, along with the increase of the dosage of ceramsite concrete early crack resistance gradually improved, the higher the moisture content of ceramsite to improve the situation, the more obvious.After mixed with nano silica, the ability to resist cracking of concrete has improved significantly.