| Steel slag has the characteristics of high hardness and good wear resistance.If steel slag is used to replace part of crushed stone in the construction of cement stabilization base,it can produce huge economic and social benefits.Due to the influence of humidity and temperature,cracking of cement stabilized base and secondary diseases are always a difficult problem in engineering.In order to enhance the crack resistance of cement stabilized steel slag gravel base,fiber is a common means.Polyvinyl alcohol(PVA)fiber has the advantages of high strength,high elastic modulus and high bond strength with cement matrix.Based on this,this paper takes cement stabilized steel slag macadamia mixture as the research object.By adding PVA fiber,the mechanical properties,crack resistance(dry shrinkage,warm shrinkage)and heavy metal leaching test of steel slag are studied in PVA fiber reinforced cement stabilized steel slag macadamia base mixture.The mechanical properties showed that the unconfined compressive strength and splitting strength of the cement stabilized steel slag crushed stone mixture reached the maximum when the content of PVA fiber was 0.06% and the particle size of steel slag replaced crushed stone was 4.75-31.5mm.XRD results show that the characteristic peaks of Ca(OH)2 weaken gradually with the increase of hydration reaction,while the characteristic peaks of dicalcium silicate and tricalcium silicate of cement hydration products strengthen gradually.The SEM test results of hydration products of the mixture showed that with the increase of curing age,more calcium silicate hydrate and calcium aluminate hydrate were generated,and the strength of the mixture gradually increased.The dry shrinkage test shows that the water loss rate,cumulative dry shrinkage strain and cumulative dry shrinkage coefficient of PVA fiber cement stabilized steel slag and crushed stone mixture gradually decrease with the increase of steel slag content and PVA fiber content.When the content of PVA fiber is 0.12% and the particle size of steel slag substitute gravel is 0-31.5 mm(steel slag accounts for 100%),the water loss rate,cumulative shrinkage strain and total shrinkage coefficient of PVA fiber cement stabilized steel slag gravel mixture are the minimum.However,when the particle size of steel slag replaced gravel is 0-31.5mm,the 7-day unconfined compressive strength only meets the requirements of secondary highways,and is not suitable for expressways or primary highways.Therefore,it is recommended to choose the scheme with 0.12% PVA fiber content and 4.75-31.5mm steel slag replacement particle size range(steel slag accounted for 67.4%).The temperature shrinkage test shows that the temperature shrinkage strain of PVA fiber cement stabilized steel slag gravel mixture increases with the decrease of temperature.With the increase of PVA fiber content and steel slag content,the temperature shrinkage strain of the mixture decreases gradually.The temperature shrinkage coefficient of PVA fiber cement stabilized steel slag and crushed stone mixture gradually decreases with the increase of PVA fiber content and steel slag content,but decreases first and then increases with the decrease of temperature.When the content of PVA fiber is 0.12% and the particle size of steel slag replacing crushed stone is 4.75-9.5mm(steel slag accounts for 21.3%),the temperature shrinkage strain and temperature shrinkage coefficient of PVA fiber cement stabilized steel slag crushed stone mixture are the minimum.Although the addition of steel slag increased the temperature shrinkage of the base,the increase was very small,far less than the reduction of the dry shrinkage of the base.Therefore,the fissile resistance of the mixture is mainly based on dry shrinkage strain.The recommended PVA fiber content is0.12%,and the replacement particle size of steel slag is 4.75-31.5mm.The precipitation of heavy metals in PVA fiber cement stabilized steel slag and crushed stone mixture was studied by inductively coupled plasma-mass spectrometry(ICP-MS).The results show that the cumulative leaching amount of Cr in PVA fiber cement stabilized steel slag gravel mixture increases with the increase of soaking time.The cumulative leaching amounts of three particle sizes of steel slag instead of gravel are 4.75-31.5mm < 0-4.75 mm < 0-31.5mm.Therefore,in order to reduce the influence factors of heavy metals,the steel slag particle size range of 4.75-31.5mm(coarse steel and fine stone)is recommended.Based on the mechanical properties,crack resistance and heavy metal leaching test of steel slag,it is recommended to replace the gravel with steel slag with a diameter range of 4.75-31.5mm.In terms of PVA fiber content selection,although in terms of mechanical properties,the PVA fiber content of 0.12% is slightly lower than that of the mixture with a content of 6%,it can meet the specification requirements of expressways and first-class highways.At the same time,0.12% PVA fiber content has better resistance to dry shrinkage and temperature shrinkage deformation than 6% mixture,and it is more significant to improve the crack resistance of cement stabilized gravel base.Therefore,0.12% PVA fiber content is recommended.. |
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