Drying and autogenous shrinkage of pastes and mortars with activated slag cement

• Published in: Cement and concrete research Vol. 38; no. 4; pp. 565 - 574
• Main Authors: Melo Neto, Antonio A., Cincotto, Maria Alba, Repette, Wellington
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Ltd 01-04-2008; Elsevier Science
• Subjects: Alkali activated cement; Applied sciences; Autogenous; Buildings. Public works; Cement concrete constituents; Cements; Concretes. Mortars. Grouts; Exact sciences and technology; General (composition, classification, performance, standards, patents, etc.); Materials; Pore size distribution; Properties and test methods; Properties of anhydrous and hydrated cement, test methods; Shrinkage; Thermal analysis; Autogenous; Alkali activated cement; Shrinkage; Thermal analysis; Pore size distribution; Mortar; Activated slag; Experimental study; Pore size; Cement paste; Calorimetry; Porosity; Comparative study; Drying
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2007.11.002

Activated slag cement (ASC) shows significantly higher shrinkage than ordinary Portland cement agglomerates. Cracking generated by shrinkage is one of the most critical drawbacks for broader applications of this promising alternative binder. This article investigates the relationship between ASC hydration, unrestrained drying and autogenous shrinkage of mortar specimens. The chemical and microstructure evolution due to hydration were determined on pastes by thermogravimetric analysis, conduction calorimetry and mercury porosimetry. Samples were prepared with ground blast furnace slag (BFS) activated with sodium silicate (silica modulus of 1.7) with 2.5, 3.5 and 4.5% of Na
2O, by slag mass. The amount of activator is the primary influence on drying and autogenous shrinkage, and early hydration makes a considerable contribution to the total result, which increases with the amount of silica. Drying shrinkage occurred in two stages, the first caused by extensive water loss when the samples were exposed to the environment, and the second was associated with the hydration process and less water loss. Due to the refinement of ASC porous system, autogenous shrinkage is responsible for a significant amount of the total shrinkage.