Research On The Drying Performance And Improving Measures Of Alkali-activated Slag Concrete

Alkali-activated slag cement is a new type of cementitious material utilized the industrial by-products as the alkaline component, it has some excellent properties, namely, low heat of hydration, high compressive strength and less requirement of energy. According to the previous investigations, alkali-activated slag concrete (AASC) had highly drying shrinkage, of which the shrinking value exceeded that of ordinary Portland cement concrete (OPCC) in most cases. Moreover, it is apparent that the workability and properties are diverse due to the type and compositions of the activator. The early researches revealed the hydration of AASC was rather different from that of OPCC and Ca(OH)2 crystal was rarely existent among the hydration products. In the research, three types of admixture were used to modify the properties of AASC, the result shows:①Liquid sodium silicate-activated slag concrete has higher shrinkage in comparison with which of AASC when NaOH,Na2CO3 are used. The shrinkage of AASC with the modulus equal to 1.5 is lower compared with the AASC of which the modulus is ranging from 1.0 to 2.0, while it increases with the increasing concentration of Na2O.②The early shrinkage decreases when w/c ratio is ranging from 0.37 to 0.45 whereas the later shrinkage increases.③The compressive strength and shrinkage of AASC decreases with the increasing dosage of expansive admixture when it ranges from 6% to 10%.④When expansive admixture are blended, the shrinkage of AASC with NaOH as the activator has a higher reducing rate in comparison with liquid-activated slag concrete. The shrinkage of AASC with higher modulus has a greater reducing rate with the increasing modulus which is ranging from 1.0 to 2.0 and the increasing concertration of Na2O which is ranging from 4% to 6%.⑤The shrinkage of AASC with 0.45 of w/c ratio has a better improvement compared with which whose w/c raito is equal to 0.37 when expansive admixture is blended.⑥The shrinkage of AASC blended with expansive admixture is lower when it is cured for 7 days compared with the one cured for 3 days.⑦Generally, alunite expansive admixture is more suitable for AASC in comparison with ZY and metakaolin.⑧The restricted expansion rate of AASC increases with the increasing dosage of expansive admixture when it ranges from 6% to 10%.⑨NaOH-activated slag concrete has higher restricted expansion rate compared with liquid sodium silicate-activated slag concrete. With the increasing modulus, concentration of Na2O and w/c ratio, the restricted expansion rate of AASC reduces slightly.⑩The restricted expansion rate of AASC decreases with the increasing w/c ratio when it is ranging from 0.37 to 0.45.