Conclusions

The fracture properties and tension softening behavior of concrete are important characteristics for structural design and analysis of concrete structures.A series of experimental tests have been conducted to investigate such behaviors of geopolymer mortar and concrete with different strength grades and material compositions.The following conclusions have been reached through the study:

(1)Given the same compressive strength,the elastic modulus of AAS mortar and concrete are generally smaller than their PC counterparts,by around 25%～35%.

(2)The fracture energy Gf of AAS geopolymer concrete increases with the compressive strength,but Gf of AAS geopolymer mortar reduces as the compressive strength increases.

(3)Given the same compressive strength,the Gf of AAS geopolymer concrete is always higher than that of PC concrete due to the denser and stronger ITZs between the AAS pastes and aggregates.However,the Gf of AAS geopolymer mortar at M30 is higher than that of PC mortar due to the more homogenous matrix and denser ITZs,and when the compressive strength further increases,the Gf of AAS geopolymer mortar is lower than its PC counterpart due to more micro-cracks occurring in the former matrix.

(4)The compressive strength of AASFC gepolymer concrete increase with the alkali concentration,the modulus and the slag/FA ratio while decrease with the increase of water/binder ratio.The 3-day compressive strength of AASFC geopolymer concrete can achieve almost 40 MPa and significant further compressive strength development can be observed after 28 days.

(5)The Gf of AASFC geopolymer concrete increases with the alkali concentration,the modulus and the slag/FA mass ratio while decreases with the increase of water/binder ratio,in other words,increases with the compressive strength.

(6)The normalized bilinear softening curves of PC concrete and AASC gepolymer concrete are generally the similar given the same compressive strength although the slope of the initial descending part of AAS geopolymer concrete is slightly smaller than that of PC concrete in the case of C30.PC mortar usually has a smaller first descending slope than AAS gepolymer mortar at all the three compressive strength levels.For both AAS gepolymer and PC concrete and mortar,the first descending slope becomes sharper with the strength increase.

(7)The normalized bilinear tensionsoftening curves of AASFC gepolymer concrete exhibit the similar first descending part regardless of the varied material parameters.For the second descending part,the alkali-concentration has the least effect.Changing the modulus from 1.0 and 1.5 leads to a marginal change of the softening curve but a further increase to 2.0 increases the freestress crack width.

(8)There seems to exist an optimal slag/fly ash ratio in terms of the Gf of AASFC GC.However,a slag/FA ratio of 50/50 and a slag ratio of 100% led to almost the identical normalized tensionsoftening curves.