Research Of Low Carbon Dioxide Emission Crack Resistance Alkali-activated Cement

Alkali-activated cement has many advantages, such as fast hardening, high early strength, low heat of hydration, and good resistance to chemical corrosion, it can recycle industrial solid waste, and has good durability, so it becomes one of the hottest research topices as a low carbon emissions concrete recently. The hydration product of alkali-activated cement is mainly C-S-H gel, and it doesn't include crystal phase nearly. The huge surface area of C-S-H gel causes significant shrinkage and crack tendency of alkali activated cement. This brings about bad outlook and durability of alkali-activated cement which is one of the mainly drawback to its widely utilization. For these reasons, the improvement of the crack resistance is the key issue to be studied to make it engineering applied.In the paper, two type of low carbon dioxide emission eco-cement.e.g. phosphogypsum modification alkali-activated slag system (PAAS) and magnesia modification alkali-activated slag fly ash system (MAAFS) were prepared, their physical properties, drying shrinkage, crack resistance and other properties of two cement are researched, the properties of concrete made of PAAS and MAAFS are studied. The mian conclusions can be draw as following:1. The optimum composition of PAAS:10% phosphogypsum+8%(in Na2O+SiO2, module=1) activator, the strength of PAAS can meet to the standard of a grade 32.5 slag Portland cement, the crack resistance of PAAS is better than that of ordinary alkali-activated cement.2. The optimum composition of MAAFS:8%(in Na2O+SiO2, module=1) activator +slag:fly ash:magnesia=36:24:40, the strength of MAAFS can meet to the standard of a grade 42.5 ordinary Portland cement, the crack resistance of MAAFS is better than that of PAAS and ordinary alkali-activated cement.3. The main hydration products of PAAS are C-S-H gel and ettringite. The ettringite crystals intersperses between the C-S-H gel, it increases the contacts of C-S-H gel and reduces the cracking of this cement due to the expansion brought about by the formation of it. The main hydration products of MAAFS are C-S-H gel, magnesium carbonate and magnesium hydroxide. The formation of Magnesium carbonate and magnesium hydroxide results in volume expansion and reduces the cracks. The porosity of MAAFS is better than Portland cement.4. The strengths of two kinds of low carbon dioxide emission crack resistance alkali-activated concrete is higher while their shrinkage rate are less than ordinary alkali-activated concrete.