3.1 Strength and Elastic Modulus
Figure 4(a)presents the average values and variations of the compressive strengths of PC and AAS geopolymer mortar(M30,M50 and M70)and geopolymer concrete(C30,C50 and C70).It is clear that both PC and AAS geopolymer mortar and concrete achieved very similar 28-day compressive strengths,facilitating a sound basis for their comparisons.The average compressive strengths were obtained from the testing results of three identical specimens in each group.The maximum strength deviation was±6.4%,indicating a good quality control.Figure 4(b)depicts the modulus of elasticity of PC and AAS geopolymer mortar and concrete.The PC concrete clearly had an elastic modulus 25%～35% higher than AAS geopolymer concrete,and for the PCM,it was also 25%～35%higher than AASM given the same compressive strength grade.With C70,the elastic modulus of PC concrete was(35.2±1.1)GPa while the elastic modulus of AAS gepolymer concrete was(23.6±1.2)GPa.The average value of the latter was 33%lower than that of the former.
Figure 4 Mechanical properties of PC and AAS geopolymer concrete/mortar
Figure 5 Parametric effects on the compressive strength development of ASFSC geopolymer concrete
The compressive strength developments of AASFC with the alkali concentration,the modulus,the water/binder ratio and the slag/FA ratio are shown in Figure 5.It is seen that the compressive strength of AASFC increased with the curing time and significant strength development could still be observed after 28 days.The compressive strength of AASFC increased with the alkali concentration,the modulus and the slag/FA ratio while decreased with the increase of water/binder ratio.The 3-day compressive strength of AASFC could achieve almost 40 MPa in many cases.The 28-day compressive strength of AASFC increased from 31.7 MPa to 58.2 MPa(i.e.an 83.6%increase)when the alkali concentration increased from 3% to 5%.The average compressive strengths of AASFC with alkali concentration of 5%were 34.7 MPa,46.0 MPa,58.2 MPa and 68.4 MPa,respectively,corresponding to the curing ages of 3,7,28 and 90 days.A further 17.5% increase of compressive strength was observed when the curing age increased from 28 days to 90 days.