| “Strengthened basecourese-thin upper layer-stable subgrade” is the conceptinsisted in pavement structure design in China, and semi-rigid pavement base is themain load bearing layer in pavement structure. High performance of aggregate is theguarantee for pavement base material performance, however, which brings aboutconfliction between resource-energy demand and increasingly serious gap. So, newpavement base aggregate discovery is the key to develop recycling economy. Becausesteel slag, which is solid residue of iron industry, shows good stiffness, abrasionresistance and hydrating harden property in a certain degree, it could be used aspavement base aggregate, premised on the steadility of immersion volumetricexpansion.This paper is aimed at the reasonable application of steel slag in lime-fly ashstabilized pavement base material. Firstly, material mix proportion design forperformance evaluation is carried out, which is on purpose to guarantee designstrength of material and stability of aggregate. Mix proportion is determined byunconfined compressive strength and immersing volumetric expansion rate ofaggregate, which is affected by aggregate gradation type, binder content, andcomposition of aggregate. Then mixture is prepared according to designed proportion,and tests on indirect tensile strength, resilient modulus, dry shrinkage, temperatureshrinkage, water scouring and freeze-thaw are conducted. Lastly, mechanism analysison material performance is made based on basic theory.Mix proportion design is based on aggregate gradation in two types: skeletonand suspension, lime-fly ash content of16%,18%,20%, and steel slag-crushed stoneproportion of0:100,25:75,50:50,75:25, and100:0. It is found in the progress ofdesign that the optimal proportion of lime-fly ash is1:3. Mixtures in differentaggregate gradation, binder content and steel-slag proportion can meet designstrength requirement that not less than0.8MPa. Yet, in the condition that steel slag ismore than50%in aggregate, immersing expansion rate is beyond the upper bound of2.0%.Gradation type and binder content is chosen the same as in design whilesteel-crushed stone proportion is limited to0:100,25:75,50:50for performanceevaluation mixture. Results from tests show that increasing ratio of steel slag in aggregate rises resilient moduli, indirect tensile strength and freeze-thaw residualstrength ratio of mixture in two different gradation types by up to16%,24%and10%,respectively, and slightly increases temperature sensitivity of mixture by up to7%.Gradation and binder content should also be considered in evaluation of materialperformance. Resilient moduli of skeleton gradation mixture shows higher value thansuspension gradation mixture at high binder content, while it performs low valuewhen binder is inadequate. Generally, suspension gradation mixture has higherindirect tensile strength than skeleton type. Dry shrinkage and temperature shrinkageof mixture rises by increasing lime-fly-ash, and generally, test resaults of skeletontype is lower than suspension type. Skeleton gradation mixture, which has optimalwater scouring resistance at18%binder content, performs better than suspension type,while scouring loss of suspension type rises with increasement of binder. Lime-flyash addition enhances freeze stability of mixture, and suspension type is slightlysuperior to skeleton type in this property.Affection of aggregate gradation, binder content and steel slag ratio onperformance of material is explained by mechanism of physic-mechanics, shrinkage,scouring and freeze stability. Test results and analysis indicate that steel slag could bea high performance pavement base aggregate, premised on the volumetric stability,and the double benefits of saving resources and protecting environment can beachieved. |
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