Effect Of New Multiple Composite Cementing Materials On Mechanical Properties And Microstructure Of PHC Pipe Pile Concrete

Prestressed high-strength concrete pipe piles are widely used in various infrastructure projects due to their reliable quality,convenient pile planting,fast construction speed,and good seismic performance of pile foundations.In recent years,its production and application have developed rapidly.However,due to the low production efficiency and the country’s increasing efforts in environmental governance,the pressure on enterprises has also increased.How to optimize the production process and improve production efficiency on the premise of ensuring the reliable quality of concrete pipe piles has become a problem that enterprises must consider.This project plans to apply new materials such as undisturbed silica fume,high calcium silica fume,densified silica fume,and coal-measure metakaolin in the production of pipe piles to improve the early strength of concrete pipe piles and save production time and cost;technology to guide the production of concrete pipe piles.This preparation technology reduces the consumption of cement resources,reduces the production cost,improves the environmental pollution problem,and greatly improves the production efficiency of pipe piles.The main research contents of this paper are as follows:（1）In order to study the mechanical properties and activity index of single doped new materials of P·O42.5 cement and P·O52.5 cement composite cementing system at various ages,P·O42.5 and P·O52.5 cement mortar specimens with single doped new materials were prepared in the laboratory stage.The flexural strength and compressive strength of the specimens for 1d,2 d,3 d,7 d and 28 d were tested,and the activity index of the new material and the strength growth factor of the test block at each age were calculated.The mechanical properties of P·O42.5 cement mortar were studied by single and compound mixing of new auxiliary cementing materials.The results show that the large amount of ore powder has a great influence on the mechanical properties of P·O42.5 cement mortar in the early stage,and the flexural strength and compressive strength are significantly lower than those of the control group,but the flexural strength and compressive strength increase rapidly with the extension of curing time.The compressive strength activity index of all kinds of new materials in P·O42.5 cement was higher in the standard curing period of 3 d,and decreased slightly with the extension of curing time.After standard curing for 28 days,the compressive strength of all kinds of cementing samples of P·O42.5 cement composite cementing system was higher than that of the control group.The influence of new material on P·O52.5 cement mortar is similar to that of P·O42.5.The bending strength of P·O52.5 cement mortar is small at each age of composite cementing system with new material,but the compressive strength is improved,and the compressive strength activity index decreases gradually with the extension of curing time.The maximum strength of test block was 61.8 MPa.（2）In order to study the mechanical properties and activity index of composite cementing system of P·O42.5 cement and P·O52.5 cement,P·O42.5 cement and P·O52.5 cement mortar specimens mixed with new materials were prepared in the laboratory stage.The flexural strength and compressive strength of the specimens at 1 d,2 d,3 d,7 d and 28 d were tested,and the activity index of the new material at each age and the strength growth factor of the test block were calculated to study the development law of the mechanical properties of P·O42.5cement mortar mixed with the new auxiliary cementing material.The results show that:New materials can make up for the influence of mineral powder on the early mechanical properties of cement mortar.When the standard curing period is from 1 d to 7 d,the activity indexes of various new materials differ greatly.With the extension of curing time,the flexural strength of experimental group is significantly higher than that of control group at 28 d,and the flexural strength is up to 8.6 MPa.P·O42.5 cement mixed with the new material also showed a higher compressive strength activity index,among which K20P8 was the best,the compressive strength of the test block reached 59.2mpa.The new compound material showed high reactivity in the composite cementing system of P·O52.5 cement.The compressive strength of experimental groups was always higher than that of the control group during 1 d to 28 d of standard curing,and the strength of K20P8 reached 66.5mpa at 28 d,18%higher than that of the control group.（3）In order to study double with three mixed new material compound gel system of steam and steam autoclaved concrete mechanical properties and the effect of adding new material of concrete specimen preparation,and combining with the production process,the concrete pipe pile using steam curing and steam autoclave curing of concrete specimen,with concrete compressive strength and compression strength against as an index,The influence of new auxiliary cementing materials with double and triple additives on the mechanical properties of steam and steam-autoclaved concrete was studied.The results show that the compressive strength of K25P5 group is the highest at steam curing for 4 h and 8 h,reaching 87.8 MPa and87.4 MPa respectively.The compressive strength of K25MG5 group is the highest at steam curing for 12h,reaching 86 MPa.The results show that the compressive strength of steam cured concrete can be improved by the new cementation materials with three mixtures.The compressive strength of K20P5MG5 is the highest after steam curing for 4 h and 8 h,and the compressive strength of K22P4HG4 group is the highest after steam curing for 12 h,reaching85.5 MPa.The compressive strength of K20P5M5 is the highest in autoclaved environment,reaching 84.6mpa.In order to study the effect of different early-strength agents on steam and steam-autoclaved concrete,concrete specimens with single/multiple admixture of sodium sulfate and sodium nitrite were prepared respectively.The dosage is 0.1%,the effect is the best,and the compressive strength is increased by 10%compared with the control group.In order to study the effect of different nanomaterials on steam and steam-autoclaved concrete,concrete specimens with single/multiple admixture of nano-Ca CO₃ and nano-Si O₂ were prepared respectively.The compressive strength also has a significant effect.The nano-materials with0.1%nano-Si O₂ and 2%（1%nano-Si O₂+1%nano-Ca CO₃）have the best improvement effect,and the compressive strength of concrete reaches 79.4 MPa and 80 MPa,which were increased by 19%and 20%,respectively,compared with the control group.（4）In order to study the silicon ash and coal measures kaolin of hardened cement paste microstructure and hydration products and the effect of using SEM to study the silicon ash and metakaolin effect of hardened cement paste microstructure,the EDS analysis of hardened cement paste than calcium silicon,using XRD spectrum research of compound gel silicon ash and metakaolin system the influence of hydration products.The results show that both silica fume and metakaolin can reduce the content of Ca（OH）₂ crystal in cement hardened slurry under steam curing environment,and metakaolin has stronger reactivity with Ca（OH）₂ and can consume more Ca（OH）₂.But the addition of silica fume or metakaolin did not change the type of hydration products.Both silica fume and metakaolin can fill large pores in cement hardened slurry and improve pore structure.By comparing the electron microscope images,it can be seen that metakaolin has better effect than silica fume and denser hardened slurry.