Experimental Study On The Effect Of Air Entrainment On Mechanical Properties And Frost Resistance Of Recycled Concrete

With the rapidly development of construction industry, more and more concrete was consumed. This caused lots of problems, such as the aggregate resource scarcity, land occupied by waste concret, environmental pollution and so on. The emergence of recycled concrete technology, effectively resolved the contradictions, and ensured the sustainable development in the industry, which has an industrializational development prospects. In China, at present the study about durability of recycled concrete is less, especially in anti-freeze durability aspect, different scholars have different conclusion. In order to expand the application range of the recycled concreteI chose recycled concrete's basic mechanical properties and anti-freeze capability as the main research direction, to study the impact of Air-entraining agent to recycled concrete.In order to research the effect of the attached mortar of recycled aggregate on properties of recycled concrete, original mortar was produced with air entrainment of 1.5% ,3%, 5%, 7%. This paper studied the influence of air entrainment to original mortar's cube and prism compressive strength, splitting tensile strength, bending strength and dry shrinkage. The results showed that, with the increase of air entrainment, the mortar's strength decreased and the shrinkage increased.The above original mortar was made into recycled coarse aggregate by crushing and screening. Technical indexes of recycled coarse aggregate were investigated according to Recycled Aggregate for Concrete (GB/T25177-2010). The test results showed that the recycled coarse aggregate was class III.Recycled concret was producted by different air entrainment recycled aggregate. By means of quick freeing and thawing test, compared with ordinary concrete, the freezing and thawing resistance of air-entrained concret when different air entrainment concret is used as recycled coarse aggregate was studied. The results showed that recycled coarse aggregate produced from air-entrained mortar caused better forst resistance in concrete ;when air content of coarse aggregate is between 5% and 7%, the recycled concret can rich the same forst resistance level as common concrete. However, if the recycled coarse aggregate is non-air-entrained, the recycled concret's forst resistance is poor,even when the new system had a proper air entrainment. The paper also got the influence of original concrete's strength on recycled concret's 7 day strents is little; 28 days later, recycled concrete's compressive strength decrease as original concret. The air entrainment of original conctet has little ipmact on recycled concrete's shrinkage properties.Optical microscopy analyzer and Scanning electron microscope were used to study the microstructure of the four different airentrainment primary mortar and recycled concrete. Find air-entraining agent can make mortar internally generate pores about 2μm. Both recycled concrete and ordinary concrete's destruction of freeze-thaw was start from interfacial transition zone. On recycled concrete, damage happened earlier in the old non-air-entrained mortar than the new air-entrained mortar.