Study On Preparation Of Green Engineered Cementitious Composites Using Alkali-activated Slag

The basic design principal of engineered cementitious composites(ECC) was founded by Prof. Victor Li from Michigan University using micro-mechanics and fracture mechanics approach. ECC is a kind of cementitious composites with strain-hardening behavior under uniaxial tension. Due to its high toughness and special multiple-cracking property, ECC has a great potential to be widely used in civil engineering. ECC has advantages in long-term properties and durability, however, its cement content is great. The large consumption of Portland cement causes resources and environmental issues. Alkali-activated slag cement, which is energy saving with excellent properties as well, is a kind of green building materials through utilization of solid waste. At present, the compressive strength of strain hardening fiber reinforced alkali-activated mortar is relatively low and has great room for improvement.In order to obtain a green ECC with higher strength and better ultimate deformation capacity, the strain-hardening fiber reinforced alkali-activated slag composites(AAS-ECC) was prepared by the combination of alkali-activated slag concrete technology and the original preparation technology of ECC. Its compressive is 2 times higher than that of AAS-ECC reported. By changing water-binder ratio(W/B), sand-binder ratio(S/B) and dosage of alkali, the effects of the three factors on AAS-ECC performance were investigated through flexural, compressive, uniaxial tensile and four-point bending tests, and then optimize the mix proportion. The main conclusions are as follows:(1) The flexural strength of AAS-ECC at age of 28 d is in the range of 9 ~ 16.9 MPa, and the compressive strength at the same age is in the range of 77.2 ~ 106.7 MPa. The flexural and compressive strength decreases with the increase of W/B, and increases with the increase of S/B. The highest compressive strength is obtained when the dosage of alkali is in the range of 6%~8%.(2) The ultimate tensile strain capacity of AAS-ECC can reach above 1%. Multiple cracking and strain-hardening behavior can be observed during the uniaxial tensile test. The various tensile property indices fluctuates with the increase of W/B, S/B and alkali content. When S/B is 0.8, W/B is 0.35 ~ 0.40 and alkali content is 4% or 8%, AAS-ECC obtains the best strain-hardening behavior.(3) The ultimate bending strength of AAS-ECC is in the range of 8.1 ~ 13.8 MPa, and the average ultimate bending displacement is 1.3384 ~ 5.4491 mm under four-point bending load. Each bending property index fluctuates with the increase of W/B, S/B and alkali dosage. The AAS-ECC with S/B of 0.4, W/B of 0.40 and alkali dosage of 10% obtains highest PSH toughness index.(4) The relationships between tensile and compressive properties, tensile and bending properties were comprehensively analyzed. The optimum mix proportion is W/B of 0.35 and S/B of 0.6 ~ 0.8, with suitable alkali content.