Relationship Between The Composition,Structure And Abrasion Resistance Of Hydraulic Concrete

The concrete surface in hydraulic structures exposed to high-velocity sediment laden water flow often suffers a severe abrasion-erosion damage.Mineral admixtures（such as silica fume,furnace slag and fly ash）have a certain improvement effect on the abrasion resistance of concrete,but it is also necessary to seek mineral admixtures with better modification effects.Concrete is a multi-component composite material consisting of paste,aggregate,and paste-aggregate interface zone.Researchs on the influence of different aggregates and different mineral admixtures on the abrasion resistance of concrete often stayed at the concrete level.And these researchs did not thoroughly analyze the wear resistance of the paste and the aggregate itself and its relationship with the micro-structure,so that the mechanism of the abrasion resistance of concrete was not thoroughly understood.Before the abrasion resistant concrete is put into use,it should be tested indoor first,and the rationality of the evaluation index is related to the reliability of the test result.However,the sandblast abrasion test used to simulate the suspension abrasion damage exist a problem that the evaluation index of the abrasion resistance is irrational.The influence and mechanism of the micro/nano mineral admixtures on the abrasion resistance of concrete were studied.Base on the grinding wheel principle,the effect of different types of mineral admixtures on the abrasion resistance of the paste was investigated,and the relationship between the abrasion resistance of the paste and the micro-structure of the paste was established.The abrasion resistance of different aggregates was investigated,and the composition and structural factors that affect the abrasion resistance of aggregates were found out.The evaluation index of the abrasion resistance of concrete under the sandblast abrasion test conditions was studied,and a reliable abrasion resistance evaluation index was proposed.These studies will provide theoretical and technical support for the selection of mineral admixtures and aggregates in abrasion resistant concrete,and provide a more reliable evaluation index for the evaluation of abrasion resistance of concrete.The main findings are as follows:1.Through the study of the abrasion resistance of concretes containing nano-SiO₂（NS）,fly ash（FA）and super fine slag（SFS）,and combining the abrasion damage mechanism,the micro-hardness and micro-morphology of paste and paste-aggregate interface,the hydration of paste,the composition of hydration products,and the polymerization degree of C-S-H,the mechanism of the above-mentioned admixtures on the abrasion resistance of concrete was analyzed.The addition of 40%SFS,5%NS,as well as 5%NS incorporating 25%FA all can improve the abrasion resistance of concrete.The addition of 40%SFS showed a best modification effect which improved the abrasion resistance of concrete by 20%.The addition of 5%NS,as well as 5%NS incorporating 25%FA showed a same modification effect which improved the abrasion resistance of concrete by 17%.As for the lower heat of hydration of the mixed-blend system,it may be better for NS to be used incorporating with FA.The addition of SFS,NS,as well as NS incorporating FA promoted the hydration of cement matrix,consumed CH to produce more C-S-H and aluminiferous hydration products,increased the degree of polymerization of silicate chains in C-S-H,so as to strengthen the micro-mechanical properties of ITZ and the cement matrix,thereby improving the abrasion resistance of the mortar matrix and the concrete.2.Through the study of the abrasion resistance of cement pastes mixed with different admixtures（silica fume,metakaolin,furnace slag powder,fly ash,steel slag powder,and limestone powder）,and combining the analysis of microhardness,hydration process of paste,composition of the hydration products,the degree of C-S-H polymerization,and the pore structure of the paste,the mechanism of the mineral admixtures on the abrasion resistance of the paste was studied.And based on these results,the composition and structural factors affecting the abrasion resistance of paste were revealed.With the addition of 10%silica fume and metakaolin,the abrasion resistance of cement pastes increased by 31%and 11%,respectively.The main reasons for the improvement of the abrasion resistance of cement pastes after adding silica fume and metakaolin included two aspects:firstly,the incorporation of silica fume and metakaolin increased the content of C-S-H in the hydration products,thereby increasing the structural uniformity and enhancing the bonding force of the paste;secondly,the paste pore size was refined,which was conducive to improve the abrasion resistance of the paste.The increase in the abrasion resistance of the paste by silica fume was higher than that of metakaolin,which can be attributed to the fact that the silica powder can better promote the hydration of the cement,resulting in a greater amount of hydration products in the paste containing silica fume than in the paste containing metakaolin.The incorporation of furnace slag powder reduced the abrasion resistance of the cement paste.At the same time,the abrasion resistance of the paste containing 40%furnace slag powder was higher than that of the paste containing 30%furnace slag powder and the paste containing 50%furnace slag powder.There were two main reasons for the decrease of the abrasion resistance of cement paste containing furnace slag powder:firstly,the furnace slag powder with lower hardness replaces the cement with higher hardness;secondly,the microhardness of the hydration product phase containing pores decreased.The content of Ca（OH）2 in the hydration products of the paste decreased gradually with the increase of the furnace slag powder content,which was an important reason for the decrease of the microhardness of the hydration product phase containing pores.The hydration activity of the paste with the mineral powder content of 40%was higher than that of the other two pastes containing furnace slag powder,and it had the smallest porosity.This may be the reason that its abrasion resistance was higher than that of the other two groups of pastes.When the mixing amount was both 40%,as for the S95 grade furnace slag powder having lower activitiy than the S105 grade furnace slag powder,resulting in a less content of hydration products in the paste,and then resulting in a lower abrasion resistance of the paste.When designing the mix proportion of abrasion resistant concrete,the mineral powder with a higher activity should be used.After using 10%fly ash to replace the equal amount of furnace slag powder in the paste containing 50%furnace slag powder,as for the hardness of fly ash is much greater than that of the furnace slag powder,the micro-hardness of the hydration product phase was reduced.The abrasion resistance of the paste was almost constant.As the early hydration heat release can be declined by the use of fly ash,the furnace slag powder can be used together when designing the mix proportion of abrasion resistant concrete.With the use of 30%steel slag powder instead of cement,the decrease in the abrasion resistance of the paste was smaller than that of the paste with the same amount of the furnace slag powder.The main reason was that the hydration product contains more Ca（OH）₂（with higher hardness）and C-S-H with strong adhesion.At the same time,the incorporation of steel slag powder makes the early hydration heat of the paste drop more obvious,so in the proportion design of abrasion resistant concrete,steel slag powder can be used to replace part of the cement.With the use of 20%limestone powder to replace cement,the wear resistance of the paste was greatly reduced,and the wear resistance was less than that of all other pastes.The reasons can be attributed to two aspects:firstly,the incorporation of limestone powder reduces the amount of cement that participates in hydration,causing the content of hydration products to decrease,resulting in a decrease in the microhardness of the hydration product phase;secondly,the hardness of limestone powder was lower than cement and all other mineral admixtures.Therefore,it is not advisable to incorporate limestone powder in the abrasion resistant concrete.In order to improve the abrasion resistance of the paste,from the perspective of the composition and structure of paste,the content of C-S-H and Ca（OH）₂ in the hydration product should be increased as much as possible,and the compaction of paste should be increased;from the perspective of the raw materials,it is suggested to use mineral admixtures with higher pozzolanic activity and hardness.3.Through testing the abrasion resistance of the five different types of aggregates（granite,basalt,marble,limestone and dolomite）under micro-cutting,combined with analysis of abrasion mechanism,microhardness,mineral composition and microstructure of rock aggregates,and microstructural factors that influence the abrasion resistance of rock aggregates were studied.Granite had the highest abrasion resistance which was about 13 times that of the dolomite with the lowest abrasion resistance;basalt had the second highest wear resistance which was about 5 times that of dolomite;the wear resistance of marble,limestone and dolomite decreased in turn,but the difference was small.The microhardness of different aggregates can reflect the wear resistance of each aggregate to a certain degree,and when the content of the mineral components with higher hardness in the rock is greater,it will have higher abrasion resistance.The porosity and grain size and morphology of aggregates will also affect the wear resistance to a certain extent.4.Two kinds of concretes with different mix ratios were selected for abrasion test.Using the sandblast test method and image analysis technology,the mass loss rate,volume loss rate,density of the material been worn and the profile of the crater on the fixed profile over time,and the apparent appearance of concrete at each characteristic time node were determined.Based on these results,the criteria for the stability of the concrete abrasion failure was studied,and a reliable evaluation index of the abrasion resistance of the concrete was thus optimized.For concrete made of mortar and aggregates with similar wear properties,the mass loss rate remained stable with time gone by,the volume loss rate gradually decreased but tended to be stable quickly,and the density of the worn material gradually increased to be consistency with the density of concrete.For the concrete whose mortar having an abrasion resistance far smaller than that of aggregate,the mass loss rate shows a stepwise decline pattern with time gone by.The mass loss rate will only enter the true stable period after experiencing the period of mortar abrasion erosion with a cliff-fall of mass loss.The volume loss rate gradually decreases and gradually becomes stable.The density of the worn material gradually increases and eventually stabilized in the density of concrete.There are three elements when the abrasion erosion of concrete is in the stable stage,including a stable mass loss rate,a stable volume loss rate,and the density of the worn material being the same as the bulk density of concrete.The stable volume loss rate is a more reliable evaluation index for the abrasion resistance of concrete.