Study Of Atmospherical Dry-heating Curing For Lime-sand Concrete Products

Traditional lime sand concrete is a kind of building material which is made of lime and sand and used autoclave curing technology.It can be used to make lime sand brick,lime sand aerated concrete and various prefabricated components.However,the use of autoclaved technology has a huge investment in equipment,high cost of construction,energy con-sumption,heavy pollution and other serious,seriously restricting the development of the industry.If you can cancel the autoclaved curing system,the use of atmospherical Dry-heating curing will greatly promote the gray sand concrete products industry development.The water-holding capacity of the lime-sand concrete is improved by adding an admixture MH.The hydration mechanism of the lime sand concrete is changed and the strength is developted.In this paper,the effects of heating rate,constant temperature and constant temperature on the ash sand concrete were studied with the mechanical properties as the index.The appropriate curing system was determined.The influence of the mixing ratio on the concrete was studied with the mechanical properties as the index.And the influence of MH content on the water retention capacity of lime sand concrete was studied.As the GBT / 2542-2012 "brick wall test method",and the mechanical properties were studied except the strength,and the performance of the non-satisfactory performance was improved.At the same time,this technology for aerated concrete was studied.At last,the micro-composition and microstructure of concrete were tested.The results show that the ratio of calcium to silicon is 0.25,the ratio of water to solid is 0.1(the total mass ratio of water to lime,sand powder and sand),the ratio of lime and sand powder quality to aggregate mass is 0.5.The maximum compressive strength of lime sand concrete reached 54.1MPa and the flexural strength reached 11.8MPa under the curing rate of 1.0 ? / min,isothermal temperature temperature of 140 ? and isothermal period for 5h.Based on GB11945-1999 "autoclaved lime-sand brick" MU25,use the mixture ratio of calcium to silicon ratio of 0.125,water-solid ratio of 0.1,cement-aggregate ratio of 0.5,and admixture of MH content of 6% to make lime-sand concrete and compressive strength reached 29.7MPa,the flexural strength reched 5.2MPa.Reference GBT / 2542-2012 "brick wall test method" in the mechanical properties other than strength indicators,tested the performance of lime sand concrete: drying shrinkage of 0.35 mm / M,meet the "autoclaved fly ash brick" JCT 239-2014 not more than 0.5mm / m requirements;freeze-thaw cycle 15 times,the quality of single pieces of the test are less than 1%,compressive strength has increased;the sample carbonization 28 days,the carbonization depth of about 50.3mm,carbonization coefficient of 0.88,meet with the "autoclaved fly ash brick" JCT 239-2014 not less than 0.85 requirements;softening coefficient of 0.48;Crystalline bloom is serious,when the admixture content decreased by 1%,the situation can be significantly improved.For aerated concrete,the results show that when the ratio of calcium to silicon is 0.25,the ratio of water to material is 0.4,the content of MH is 9%,the content of hydrogen peroxide is 2%,the content of calcium stearate is 0.5%,slurry stability of the casting is fine.The compressive strength of aerated concrete is only about 1.5MPa at the heating rate of 1.0 ? / min,constant temperature temperature of 140 ? and constant period for 5 h.Analysis of the reasons,it maybe lime due to loose and porous of itself.XRD microanalysis shows that the main products of lime sand concrete are NaCaHSiO4,Na2Ca2Si2O7 · H2 O and zeolite hydration products.SEM analysis shows that the hydration products are sheet-like cross-linking the aggregate and unreacted sand powder,further drying and dehydration after the formation of hardened body.