Evaluation Method On The Internal Curing Effect Of Self-Compacting Concrete By Pre-Wet Lightweight Aggregates

High-strength concrete has failed in traditional external curing methods,due to the low water-to-binder ratio and poor permeability.Concrete internal curing technology is an effective way to solve this problem.However,at present,there is a lack of uniform standards for the evaluation method of the internal curing effect in concrete.Therefore,it is of great theoretical value and engineering application significance to further study and improve the internal curing technology of concrete,establish the evaluation method of internal curing to improve the performance of various aspects of concrete,and promote the sustainable development of China’s construction industry.In this paper,the internal relative humidity,compressive strength,permeability and frost resistance of the concrete are selected as the evaluation indexes of the internal curing effect,and the effect of the pre-wet light aggregate content and particle size distribution on the above performance and indexes of the internal curing concrete are studied.The main work content and conclusion of the paper are as follows:(1)The basic properties(water absorption rate and water release rate)test of light ceramsite lightweight aggregate and fresh concrete and workability test were carried out.The measured 72-hour water absorption rate of light aggregates with 1-5 mm and 5-10 mm particle diameters was 18.6% and 11.7%,respectively,and the water absorption rate shows two-stage schematic.The water absorption in the first 2 hours accounted for 67% of the total water absorption Around,the water absorption performance is good.Under 97.3% relative humidity environment,the water release rate of 1-5mm lightweight aggregate is 80.12%,and the water release rate of 5-10 mm lightweight aggregate is 78.25%,indicating that the water release effect of 1-5mm light aggregate is better.After mixing with 1-5 mm particle size lightweight aggregate,the workability of concrete decreases by about 7.1% compared with ordinary concrete.As the amount of light aggregate increases,the workability decreases.5-10 mm particle size lightweight aggregate internal curing concrete and workability schematic is similar,but the reduction is greater,about 12.9%.The reason for the reduced workability lies in the gap between the particle size distribution of light aggregate and ordinary aggregate and the water absorption effect of lightweight aggregate.(2)The internal relative humidity schematic test of 14-day lightweight aggregate internal curing concrete and the concrete compressive strength tests of 7,14,28,and 60-day were carried out.The internal relative humidity of all concrete groups showed four-stage schematic.The schematic of released water volume changes with time is similar.Lightweight aggregate will release internal curing water,increase humidity,and timely replenish the water consumed by cement hydration.Lightweight aggregate is a weak point.After concrete is mixed,the strength decreases by 2.1-17.7% before 28 days.As the amount of lightweight aggregate increases,the decrease increases.The strength growth rate of each group of specimens before 28 days was basically the same.After 28 days,the beneficial effect of internal curing with 1-5 mm particle size lightweight aggregate on concrete strength gradually appeared.Due to the increased degree of hydration in the later period,its compressive strength beyond ordinary concrete,the 60-day strength growth rate reached 31.27% and 31.02%,respectively.(3)The capillary water absorption test and anti-chloride ion penetration test of internal curing concrete were carried out,and tested concrete capillary water absorption rate and unsteady state chloride ion migration coefficient.The experiment found that the capillary water absorption process of the concrete internal curing in lightweight aggregate showed two-stage schematic: the initial stage and the late adsorption stage.Due to the further hydration of the concrete,the capillary water absorption rate of the internal curing concrete differed by 40% between the 28-day and 60-day ages.The 28-day initial water absorption rate of the group mixed with lightweight aggregate and ordinary concrete is about 0.8-9.3%.The internal curing of the two types of lightweight aggregates reduced the initial water absorption of concrete by about 16-28% for 60 days.However,the effect of blending amount on initial water absorption is not obvious.The effect of the internal curing of lightweight aggregate on the water absorption of the concrete in the later period is different from that in the early stage: the addition of lightweight aggregate improves the water absorption of the concrete in the later period of 28 days and 60 days,and increases with the increase in particle size and amount.The reason is the change in the pore structure of the concrete.The internal curing of the two types of lightweight aggregates significantly improved the resistance to chloride ion penetration of 28-day concrete,and the unsteady state chloride ion migration coefficient was reduced by 15.3-31.7%.The internal curing of 1-5 mm particle size lightweight aggregate still improved the resistance of concrete to chloride ion penetration by 12.1-18.2% for 60 days,due to the increased degree of hydration.With the carrier effect of lightweight aggregates,5-10 mm particle size lightweight aggregates have a detrimental effect on the 60-day concrete resistance to chloride ion penetration,and as the amount of lightweight aggregate increases,the negative effects become more obvious.(4)The rapid freeze-thaw cycle test of internal curing concrete was carried out,the change of the relative dynamic elastic modulus of the concrete and the mass loss rate were measured,and the relative durability index was calculated.The 28-day relative dynamic elastic modulus and relative durability coefficient of concrete reached 85% or more,and the mass loss rate of all concrete groups during the circulation process was below 2.8%.The internal curing of 1-5 mm particle size lightweight aggregate significantly improves the frost freezing performance of concrete,which is due to the increased degree of cement hydration and air entrainment.However,the improvement effect of 5-10 mm particle size lightweight aggregate is not obvious.As the amount of lightweight aggregate increases,the relative dynamic elastic modulus of concrete decreases.