Influence Of Water Absorption Characteristics Of Tuff Machine-made Sand On Properties Of Cement-based Materials And Pore Structure Analysis

The water absorption characteristics of tuff machine-made sand are different from those of natural sand,which has a significant impact on the properties of cement-based materials.Most of the existing standards and research focus on the effects of factors such as gradation,stone powder,and particle size on the cement-based materials of machine-made sand.Although some of the characteristics of machine-made sand are accurately characterized,they are not comprehensive,and there is a lack of research on the water absorption characteristics of machine-made sand.Based on this,this paper studies the comprehensive characteristics of tuff machine-made sand with reference to standard sand,river sand and granite machine-made sand,and focuses on the influence of water absorption characteristics of tuff machine-made sand on the performance of cement-based materials.After studying and analyzing five kinds of tuff machine-made sand produced in different regions of Zhejiang Province,it is found that the tuff machine-made sand selected in this study has little difference in such parameters as stone powder content,MB value,bulk density and void ratio,crushing index,but has great difference in particle size grading and saturated surface dry water absorption.The content of particles with the particle size of 1.18 mm and above and less than 0.15 mm in the machine-made sand of each tuff is much higher than that of river sand,and the content of particles with the particle size of 0.6mm and 0.3mm is much lower than that of river sand,showing a grain grading pattern of more at two ends and less in the middle.The content of particles with the particle size of 1.18 mm and above and0.15 mm and below in machine-made sand of different tuff varies greatly.The saturated surface dry water absorption of tuff machine-made sand is greater than that of river sand.However,due to the different characteristics of parent rock and production technology,the saturated surface dry water absorption of tuff machine-made sand varies greatly.By controlling the same mix proportion,the influence of tuff machine-made sand on the performance of mortar and concrete is explored.The test results show that compared with river sand mortar,the fluidity of tuff machine-made sand mortar decreases by 8%～38%;Compared with river sand concrete,the slump of tuff machine-made sand concrete decreases by 28%～75%,and the expansion decreases by13%～26%.Compared with river sand mortar and concrete,the 28 d strength of tuff machine-made sand mortar and concrete is improved;Compared with river sand mortar,the early shrinkage and water evaporation of tuff machine-made sand mortar increase;Compared with standard sand mortar,the porosity of tuff machine-made sand mortar is larger,the most probable pore diameter is smaller,and the proportion of mesopore is larger.In order to eliminate the influence of particle grading and stone powder factors,this study unifies the grading of machine-made sand and river sand based on the standard sand grading,and analyzes the influence of grading adjustment on the performance of tuff machine-made sand mortar.The test results show that:(1)at the same gradation,compared with river sand mortar,the workability of tuff machine-made sand mortar is reduced,the mechanical properties are improved,the early shrinkage is increased,the most probable pore size is reduced,and the distribution of mesopores is increased;(2)The water absorption characteristics of tuff machine-made sand are closely related to the particle grading.Grading adjustment will reduce the absorbed water content of tuff machine-made sand,but the impact on the absorbed water content is related to the water absorption capacity of different machine-made sand particles with different sizes.After grading adjustment,the working performance of tuff machine-made sand mortar decreases greatly with the increase of saturated surface dry water absorption,and its mechanical properties decline significantly.The effect of gradation adjustment on the early shrinkage of machine-made sand mortar for different tuff is different,which reflects the multiple effects of gradation adjustment on slurry moisture and fine aggregate skeleton.Grading adjustment has no significant impact on the porosity of tuff machine-made sand mortar,but has significant impact on the most probable pore size and the distribution of mesopore,which is manifested in the reduction of the volume of the most probable pore size and mesopore.