| In order to reduce the consumption of natural resource,emissions of carbon dioxide and costs,fly ash and slag are often used as supplementary cementing material in concrete.But distribution of resources,relatively limited production and wide range of quality fluctuations are major problems.As a supplementary cementing material,the limestone powder(LP)makes a remarkable economic and social benefits as its low price and stable composition.LP has an influence on hydration,microstructure and durability of cement-based materials.LP and supplementary cementitious materials with aluminum phase in cement-based materials have synergistic effect.Many scholars did a lot of research on the mechanism and macro performance of LP in cement-based materials,but mostly focused on the qualitative analysis.Thus,this paper adopts three pyramid orthogonal design method,and studies the synergistic effects on the hydration,microstructure and durability in cement-based materials with LP,fly ash and slag.Firstly,this paper studies the effects of LP on hydration and microstructure.The liquidity,heat of hydration,strength,hydration products and pore structure of cement-based materials are quantitative analyzed.Filler effect and chemical combination are also calculated.The results show that the hydration process of Portland cement was affected by the physical and chemical effect of LP.The size of 650 m2/kg LP and the addition of 10%LP have a great effect on the flowability and strength of cement-based materials.The increase in the content and the surface area of LP from 500 m2/kg to 950 m2/kg strengthens the nucleation effect of LP,shortens the acceleration period,increases curve slope of the acceleration period.Compared with the addition of LP,hydration is faster,total heat release is more,and the reactivity of LP is improved as for the synergistic effects of fly ash,slag and LP,when mixed with LP and supplementary cementitious materials.The increase in LP content and surface area speeds up the generation of calcium-carbonaluminates.Compared with the addition of limestone powder,the porosity in cement-based materials at 180 days respectively reduces 12.7%and 26.5%,the consumed CaCO3 content at 90 days rises up to about 4 times,the chemical reaction degree of CaCO3 is improved,and the generation of calcium-carbonaluminates is promoted when mixed with fly ash and slag.The LP surface area increases from 500 m2/kg to 950 m2/kg,the normalized chemical reaction proportion of CaCO3 at 3 days increases,rising to 2.5 times.Compared with the addition of 50%LP,the normalized chemical reaction proportion of CaCO3 at 180 days rises from 4.29%to 21.63%when mixed with 25%LP and 25%slag,rising to 4 times.In addition,this study analyzes the effects of the surface area,the content and the synergy with supplementary cementing materials of LP on the strength,carbonation and chloride permeability of concrete.The results show that the size of 650 m2/kg LP and the addition of 10%LP have a great effect on the strength,carbonation and chloride permeability of concrete.The strength,carbonation and chloride permeability of concrete have the optimal effect with 5%-15%LP and 10%fly ash,or 5%-15%LP and 25% slag. |
