Tuff Adsorbability And Effect Of Manufactured Sand On Concrete Properties

With the acceleration of urbanization and the continuous improvement of infrastructure,the huge consumption of concrete leads to the extreme shortage of natural sand resources,and manufactured sand becomes the main construction sand.Manufactured sand parent rock is generally divided into calcareous rock and siliceous rock.Among calcareous rock and siliceous parent rock,construction limestone and construction tuff are mined in the largest quantities respectively.The influence of tuff manufactured sand and tuff manufactured sand on the working performance of concrete mix is very different.At present,the national standard and the standard reduce the adsorption of tuff manufactured sand by limiting the content of tuff powder,which not only does not reflect the characteristics of tuff manufactured sand but also causes the waste of tuff powder.Therefore,scientific utilization of tuff manufactured sand and tuff powder is the key to solve the problem.In this paper,the adsorbability of tuff manufactured sand and its compatibility with water reducing agent are studied,tuff stone powder is used to replace mineral admixture to prepare cementing system,and the influence of typical lithologic tuff manufactured sand on the properties of mortar and concrete is explored.The main research contents and conclusions are as follows:(1)Experiments on methylene blue,saturated surface dry water absorption and contact Angle were carried out to compare the adsorption properties of five different tuffs.It was found that the adsorption properties of tuff powder could be characterized by referring to the MB value determined by JG/T 568-2019 "Aggregate for High Performance Concrete".The MB value determined by referring to GB/T 14684-2022 "Sand for Construction" can characterize the overall adsorption property of tuff manufactured sand.Through the compatibility test of tuff manufactured sand and water reducing agent,it is found that the dosage of water reducing agent increases with the increase of tuff adsorption and stone powder content when reaching the same expansion degree.Among the three kinds of ether and ester superplasticizers,tuff manufactured sand has the best compatibility with macromolecular ether superplasticizers.(2)Through petrographic analysis and surface morphology observation,it is found that the mineral composition and internal structure of tuff are the main reasons for its high adsorbability.Tuff contains shelf-like and stratified minerals and is prone to interchain fracture adsorption and cation adsorption in interlayer domain.At the same time,the tuff is formed by the accumulation of pyroclastic material,and its internal structure is loose and porous,resulting in high adsorption.(3)The effects of tuff manufactured sand as fine aggregate and stone powder as mineral admixture on the properties of mortar under three cementing systems were compared.Among them,cement-slag-stone powder(C-S-SP)and cement-fly ash-stone powder(C-F-SP)cementing material system have great differences in various properties of mortar,and cement-slag-fly ash-stone powder(C-S-F-SP)cementing material system has better comprehensive properties.The working performance of mortar in the low adsorption group is better than that in the high adsorption group,while the compressive and flexural strength of mortar in the low adsorption group is lower than that in the high adsorption group.(4)The influence of tuff manufactured sand on the working and mechanical properties of concrete in C-S-F-SP cementing material system is studied.When the content of stone powder is less than 30%,it meets the working requirements of concrete in flow state.The early-age strength of the two tuff manufactured sand concretes develops quickly,while the long-age strength develops slowly.Both of them meet the compressive strength requirements of C50 concrete.(5)The carbonation resistance and chloride ion penetration resistance of tuff manufactured sand concrete under C-S-F-SP cementing material system are studied.It is found that the carbonation resistance of concrete under C-S-F-SP cementing material system can be improved by extending curing age,but it is still lower than that of pure cement system.The chloride ion penetration resistance of C-S-F-SP concrete has little difference with that of pure cement control group.The compressive strength of concrete is positively correlated with the chloride ion penetration resistance,and the higher the strength,the better the chloride ion penetration resistance.