Effect And Analysis Of Adding Porous Water Retaining Material To Curing Concrete Performance

The internal curing of concrete is a kind of curing method which can effectively avoid shrinkage and cracking of concrete in the process of curin,the widely used internal curing materials are mainly porous lightweight aggregate(LWA),super absorbent resin(SAP),shrinkage reducing agent(SRA),but every kind of material in the process of use will appear to affect the performance of concrete defects.For example,the addition of LWA will affect the mechanical properties of concrete to some extent,further study is still needed on how to maintain other properties of concrete under the premise of maintaining internal curing effect;For SAP,the physical properties of SAP,such as water absorption,particle size,water release rate and so on,are affected by different preparation processes,raw materials,and the way in which SAP is added to the concrete will also affect the performance of the concrete.In addition,it is also a problem that how to control the property of SAP,in the course of construction and how to control it in the process of transportation.For SRA,current research indicates that the co-use of SRA with most admixtures will affect other properties of concrete,and that the effect of using the same type of SRA with different SAP and LWA is completely different.Therefore,when SRA and other admixtures are used together,the relevant research should be prepared in advance,and the dosage and proportion of raw materials should be strictly controlled.In view of the deficiency of internal curing materials at present,a new type of internal curing materials was prepared in this paper.Through improving the ratio of materials,preparation conditions and properties testing,a kind of internal curing material,silicon porous water-retaining material,with water content up to 85.9%,excellent water retention and release performance.After testing the contact angle of the dried porous silicon water-retaining material,it is found that the material has good hydrophobicity.It can be concluded that the porous silica retaining material after drying of water release will hinder the outside water from entering into the concrete interior,and has positive significance for enhancing the durability of concrete.Secondly,the macroscopic performance test of volume stability,mechanical properties and durability of the inner curing concrete with silicon porous water-retaining material is mainly carried out.The results show that: In terms of volume stability,the shrinkage of mortars introduced with additional water through the addition of porous silica retaining materials is lower than that of mortars that directly increase the amount of mixed water,resulting in a maximum reduction of 18%.The shrinkage of concrete at 56 days of age can be reduced by 24% by adding appropriate amount of silicon porous water retaining material;In terms of mechanical properties,the compressive strength and flexural strength of Portland cement concrete with standard curing age of 28 days can be increased by 9% and 15% respectively.The compressive strength of concrete of cement-fly ash binary cementitious material system is increased by 5.8%,and the compressive strength of concrete of cement-silica fume binary cementitious material system is increased by 8.1%.Under natural curing conditions,the concrete compressive strength of Portland cement system increased by 21.7%,and the concrete compressive strength of cement-fly ash and cement-silica ash binary cementitious materials system increased by 14.9% and 15.2% respectively;In terms of durability,the addition of silicon porous water-retaining material increases the water seepage pressure of concrete under standard curing by 25%,the carbonation depth is reduced by 33.3%,and the concrete mass loss rate after 300 freeze-thaw cycles is reduced by 31%,Strength loss reduced by 88%.The microscopic analysis methods of low-field nuclear magnetic test,X-ray diffraction(XRD)and scanning electron microscopy(SEM)were used to study the pore structure and hydration product changes during the curing process,and the microcosmic mechanism of the change of macro-performance of concrete is analyzed.Micro-experimental results show that the addition of silicon porous water-retaining material can make the unreacted water inside the concrete fully exist in the capillary pores for a period of time,avoiding the generation of capillary pressure and thus reducing the shrinkage and cracking of concrete;By comparing the XRD patterns of concrete samples of different ages,it can be found that the addition of silicon porous water-retaining materials can increase the amount of hydration products of concrete,the newly generated hydration products can still be found by observing the SEM images of concrete with porous silica-containing water-retaining material at the age of 60 d,combined with the low field nuclear magnetic test,it is found that the porous silicon water-retaining material not only reduces the porosity of the concrete,but also improves the pore proportion of the small pores in the concrete and refines the pore structure of the concrete.The microscopic test results show that the new internal curing material-silicon porous water-retaining material is added to the concrete,and the internal curing effect can effectively control the shrinkage and cracking of the concrete,the hydration degree of the cement and the compactness of the concrete are improved,and the pore structure of the concrete is optimized,thereby improving the mechanical properties and durability of the concrete.