Study On The Core Effect In SAP Aggregate Concrete

Lightweight and high strength concrete is an important development direction of cement concrete.According to the "Core Hypothesis" of Academician Wu Zhongwei,most of these introduced pores are negative core,which will affect the strength of concrete.How to weaken the "Negative Core Effect" of pore and expand the " Positive Core Effect " of the interface transition zone around the porosity is a scientific problem to be solved in the realization of lightweight and high-strength concrete.In response to this question.In this paper,the concrete was prepared by using spherical SAP aggregate with water-absorbing and water-releasing characteristics.After water release,spherical macropores with dense ITZ were formed.By improving the bearing capacity of ITZ to affect the “Negative Core Effect” of pores,a new idea of lightweight and high-strengthening concrete was formed.The main research work and research results carried out in this paper are as follows: A single SAP aggregate cement mortar was prepared.The enhancement of various spherical SAP aggregates of different particle sizes(6mm-20mm)in different matrix water-cement ratios(high-strength matrix,medium-strength matrix,low-strength matrix)were studied.Studies have shown that the internal curing enhancement effect of SAP aggregates is affected by the age of curing and the water-cement ratio.At 3d age,only the high-strength matrix group and the low-strength matrix group have partial cement aggregates(6mm,8mm)cement mortar strength higher than the blank matrix strength;and at 28 d age,the SAP aggregates are introduced.The strength of mortar exceeds the blank matrix.The lower the water-to-binder ratio,the more obvious the internal curing enhancement effect of the SAP aggregate.The concept of “Critical Dimension” of the SAP aggregate is proposed,that is,the size of the corresponding resin aggregate when the compressive strength of the SAP aggregate test block is equal to the compressive strength of the blank matrix test piece.The “Critical Dimension” of SAP aggregates of different ages is related to the water-cement ratio of mortar and the age of curing;at 7d age,the “Critical Dimension” of the low water-cement ratio mortar is the largest,which is 14.4mm;at 28 d age,the high water-cement ratio of the mortar base group has the largest “Critical Dimension” of 18 mm.The enhancement of ITZ,which also called as “Positive Core Effect” of SAP aggregate was proposed as the difference between the compressive strength of SAP aggregate cement mortar with the same particle size and the compressive strength of EPS particle cement mortar.The “Negative Core Effect” of a single hole was positively correlated with the size of the porosity.When the radius of the porosity and the side length ratio of the mortar sample were greater than 0.15,the “Negative Core Effect” of the porosity increased more significantly.When the r/L reached 0.25,the strength of the sample was only 60% of that of the blank matrix.When the size of SAP aggregate is larger than the "Critical Size",the “Positive Core Effect” of SAP is subject to the effective internal curing efficiency and decreases with the increase of particle size.The characteristics of the ITZ around the SAP aggregate were analyzed by means of microhardness,mercury intrusion analysis and hydration degree.The study found that the low-water-gel has a higher microhardness than the matrix,the interface transition zone size is smaller,and the pore structure improvement effect is more prominent: after curing for 28 days,the internal curing effect of the resin aggregate can improve the hydration degree of the ITZ and Porosity,the hydration degree of the ITZ of the high-strength matrix group is 5% higher than the hydration degree of the matrix,and the porosity is reduced by 1.7%.The hydration degree of the ITZ of the strength matrix group is 3% higher than that of the matrix,and the porosity is reduced by 0.6%.By numerical simulation and experiment,it is verified that the existence of "Shell Structure" can improve the elastic modulus of the hole-containing test block.The elastic modulus of the SAP aggregate test block is about 2 GPa higher than the elastic modulus of the EPS aggregate sample.The relationship between the spatial distribution and the strength of the SAP aggregate was explored by means of simulation calculation.The reasonable spatial distribution can increase the elastic modulus of the sample under the same SAP aggregate content.