Experimental Study On Mechanical Properties And Meso-structure Characteristics Of Stone Powder Concrete

For the growing construction of large-scale concrete projects,there is an increasing demand for the fly ash,a conventional admixture for concrete.In some areas,such as Southwest China and economically underdeveloped countries,the transportation cost of fly ash is relatively high,and it is even impossible to obtain enough fly ash and other admixtures to meet actual engineering applications.In addition,in some areas where the stone processing industry is very developed but the thermal power generation is relatively weak,the waste stone powder produced by the stone processing cannot be better recycled.Therefore,it is very important to find new admixtures that can replace fly ash,are easy to obtain,have high quality and low price,and can also be made on-site in combination with the actual project.This paper selects limestone,red sandstone and tuff for comparative analysis and research.The grinding characteristics,physical and chemical performance indexes of the three kinds of rocks,and the performance of the mortar specimens were tested and analyzed.Then the different lithology,content,and fineness of the three kinds of stone powders when mixed into the concrete were compared and analyzed.The performance and the law of change of the stone powder concrete were studied.Finally,the meso-structure characteristics of the specimens were analyzed by scanning electron microscope(SEM)observation and mercury intrusion test.The main research content and conclusions of this paper are shown as follows:(1)Three kinds of rocks of limestone,red sandstone and tuff were crushed and mechanically ground to study their grinding characteristics.The test showed that the grinding of limestone,red sandstone and tuff accorded with the grinding kinetics equation and the RRB equation.The order of grinding efficiency was:red sandstone>tuff>limestone.(2)The basic performance test and analysis of the three kinds of rock powder after grinding were carried out.The water reduction effect of limestone powder was the most significant,with a minimum water demand ratio of 95%;while red sandstone powder and tuff powder had no water reduction effect,and the water demand ratio of red sandstone powder in each fineness was greater than that of tuff powder.(3)The cement mortar tests were carried out on limestone powder,red sandstone powder and tuff powder.The strength of the three kinds of mortar samples first increased and then decreased with the increase of the content of stone powder.When the content was 20%,the strength of the three kinds of mortar samples all reached the maximum value.On the other hand,as a whole,the strength of stone powder mortar specimen increased gradually with the increase of stone powder fineness,and the increase of grinding fineness was beneficial to the activation of stone powder activity,so as to improve the strength value of stone powder mortar specimen.(4)In the experiment of mixing limestone powder,red sandstone powder and tuff powder into concrete,through detailed comparison,the influence law of the lithology,fineness and mixing amount of the three kinds of stone powder on the working performance and basic mechanical properties of concrete was analyzed.When stone powder was mixed with fly ash,the optimal dosage of stone powder is 30%～50%.The optimum dosage of stone powder was 10%～20%.When the proportion of stone powder increases from 0%to 20%,the strength of stone powder concrete increased gradually.When the mixture of stone powder and fly ash was 50%,the strength of concrete with stone powder increased by 35.7%compared with the base group.The fineness of stone powder had the same effect on the working and mechanical properties of concrete.With the increase of the fineness of stone powder,the fluidity of stone powder concrete increased,the working performance continues to improve,and the strength showed an increasing trend.However,when the fineness of stone powder increased to 10%(45μm residual),its influence on the working performance of concrete was limited or even deteriorates.(5)The meso-structure of the stone powder concrete was analyzed.The SEM photos showed that the meso-structure was improved after adding aragonite stone powder.There were more hydrated calcium silicate gel on the surface of the stone powder particles,and the porosity was relatively unmixed.The reference group of stone powder had declined,and the compactness of the specimens had increased.The micro-nucleation of stone powder particles and the reaction of volcanic ash activity with cement hydration products could promote cement hydration,reduced the content of Ca(OH)2 in hydration products,improved the compactness and porosity of mortar sand specimens,thus improving the mechanical properties of mortar sand specimens and concrete specimens.From the above research,it can be known that stone powder is mixed into concrete as an admixture in a certain proportion,which can improve the performance of concrete to a certain extent,and can meet the specification requirements for the application of stone powder in concrete.Taking stone powder as admixture in the application of concrete to conduct in-depth and extensive research,on the one hand it can alleviate the lack of concrete admixture,on the other hand,it provides an important theoretical basis for the promotion of stone powder concrete engineering.