Research On The Application Of Gangue Aggregate In Ready-Mixed Mortar

As a large coal base in China,Inner Mongolia Autonomous Region mainly discharges coal gangue,which not only occupies land,but also spontaneously emits toxic gases.As a commonly used building material,ready-mixed mortar mainly uses natural sand and limestone manufactured sand as fine aggregate at present,while excavating river sand and mining limestone mine will cause different degrees of environmental damage.Therefore,the study of coal gangue aggregate for ready-mixed mortar has significant economic and ecological environmental benefits.In this study,the typical coal gangue in Inner Mongolia Autonomous Region was taken as the research object,and its application effect as aggregate in ready-mixed mortar was studied.The effect of coal gangue aggregate and standard sand and limestone machine-made sand on the performance of ready-mixed mortar was studied.The synergistic matching of admixtures under the optimal ratio of coal gangue was further studied,and the synthesis and mechanism of coal gangue-based ready-mixed mortar were revealed.The conclusions are as follows :(1)Under the condition that the proportion of coal gangue aggregate is 60%,the 2 h consistency loss rate of ready-mixed mortar prepared by coal gangue and standard sand is20.61%,the water retention rate is 86.10%,the apparent density is 1707 g/L,the setting time is 8.25 h,the 7 d compressive strength is 8.4 MPa,the 28 d compressive strength reaches 12.3 MPa,and the 14 d bond strength reaches 0.26 MPa.The performance basically meets the requirements of M10 ready-mixed plastering mortar in the national standard(GB/T 25181-2019).(2)Under the condition that the proportion of coal gangue aggregate is 60%,the 2 h consistency loss rate of ready-mixed mortar prepared by coal gangue and limestone machine-made sand is 0.11%,the water retention rate is 84.16%,the apparent density is1742 g/L,the setting time is 8.25 h,the 7 d compressive strength is 6.2 MPa,the 28 d compressive strength reaches 12.6 MPa,and the 14 d bond strength reaches 0.29 MPa.The performance basically meets the requirements of M10 ready-mixed plastering mortar in the national standard(GB/T 25181-2019).(3)The additive reinforcement test was carried out with 60% coal gangue+40%limestone aggregate.The results showed that among the three additives,hydroxypropyl methyl cellulose had the greatest influence on the performance of mortar,followed by retarder and water reducer,and the air entraining agent had the least influence.By adding hydroxypropyl methyl cellulose 75 mg/kg,air entraining agent 80 mg/kg,retarding water reducing agent 60 mg/kg,the water retention rate of mortar increased by 10.44%,reaching94.60%.The 7 d compressive strength increased by 3.8 MPa,the 28 d compressive strength increased by 2.8 MPa,and the 14 d bond strength increased by 0.07 MPa.The 7 d compressive strength,28 d compressive strength and 14 d bond strength reached 6.2 MPa,12.6 MPa and 0.29 MPa,respectively.The properties fully meet the requirements of M15ready-mixed plastering mortar in the national standard(GB/T 25181-2019).(4)The mechanism research shows that the hydration products such as calcium silicate,calcium hydroxide,hydrated calcium silicate gel,calcite,ettringite and hydrated calcium sulphoaluminate formed by the decomposition of ettringite are formed after the hydration of coal gangue mortar.The more hydrated calcium silicate gel,ettringite and hydrated calcium sulphoaluminate generated by the mortar,the less calcium hydroxide and calcite generated,and the more stable structure formed by interconnection,the higher the strength.(5)According to preliminary calculations,the production cost of ready-mixed mortar with 60% coal gangue aggregate is 60 yuan/ton lower than that of natural sand mortar,and 30 yuan/ton lower than that of limestone machine-made sand mortar.Therefore,the application of coal gangue as aggregate to ready-mixed mortar has significant economic benefits,and to a certain extent,it reduces the stock of coal gangue,avoids its spontaneous combustion,reduces carbon dioxide emissions,and has obvious ecological and environmental benefits.