Study On The Performance Of Cement Concrete With Tuff Manufactured Sand

The lack of natural river sand has caused the demand for manufactured sand to increase day by day.It is imperative to replace natural sand with manufactured sand as the fine aggregate of concrete.On November 11,2019,ten departments including the National Development and Reform Commission,the Ministry of Industry and Information Technology,and the Ministry of Transport jointly issued the "Several Opinions on Promoting the High-Quality Development of the Mechanism Sand and Stone industry” proposed to advocate the production of highquality sand and gravel.It promoted clear requirements such as intelligent sand and gravel manufacturing,aimed at leading the high-quality development of the manufactured sand and gravel industry,and developing sand and gravel as an independent industrial system.In this paper,two strength grades of C30 and C50 were selected.The ring cracking test method and the traditional shrinkage test method were used to explore the early shrinkage cracking trend and influencing factors of the tuff manufactured sand concrete.At the same time,the workability,mechanical properties and durability of the tuff manufactured sand concrete were systematically assessed.The tuff manufactured sand produced in Gansu area was selected as the main fine aggregate.The particle size distribution,morphological characteristics and chemical compositions of tuff manufactured sand powder,Portland cement and fly ash were analyzed.Then XRD tests were performed on the pure slurry specimens with different tuff powder content that were cured to various ages.The results showed that the tuff powder promoted the early hydration of cement to a certain extent,and provided theoretical support for the macro-scale performance of concrete.According to the test results of the performance of manufactured sand concrete,the four parameters of tuff powder content,natural sand mixing ratio,water-reducing agent dosage,and manufactured sand gradations are factorial designed to systematically study the influences on the performance of manufactured sand concrete.Compared with natural river sand concrete,the optimized tuff manufactured sand concrete mix proportion can be proposed based on its engineering-based performance.The test results indicated that:(1)For 100% tuff manufactured sand concrete,5% stone powder content was optimal for workability and strength.With the increase of stone powder content,the sulfate erosion resistance and permeability performance gradually decreased and the shrinkage and cracking potential started to increase dramatically.The limit on the content of stone powder should be strictly controlled;(2)Although the 100% tuff manufactured sand concrete was not as good as the all-natural sand concrete with the same mix proportion in terms of workability,it performed better in mechanical properties and durability,exhibiting better engineering and economical benefits.(3)With the considerations of comprehensive engineering performance,a combination of30% natural sand and 70% tuff manufactured sand was recommended to apply for engineering practice based upon the performance assessed in this study.