Effect of Lightweight Aggregate on Early-Age Cracking of Mass Concrete Schindler and Tankasala, Auburn University

Early-age cracking in mass concrete structures is a severe problem that can lead to long-term serviceability problems. Researchers at Auburn University conducted a study to evaluate the effects of using lightweight aggregates on the early-age cracking tendency of mass concrete.

A considerable amount of heat is generated by the hydration of cementitious materials. As a result, there is a significant temperature differential between the interior and exterior of mass concrete elements during the early stages of construction. These temperature differences can lead to thermal cracking at an early age. Effective control of early-age cracking can result in more durable concrete and extended service life of concrete structures. This study investigated the effects of lightweight aggregates on the concrete properties that influence early-age cracking tendencies in mass concrete, compared to control mixtures containing only normal weight aggregates. Concretes with water-cementitious materials ratios of 0.38 and 0.45 were evaluated.

The results of the study indicate that using lightweight aggregates in mass concrete can improve its resistance to early-age cracking. Although increasing the amount of lightweight aggregate in the concrete mixture results in an increase in the maximum concrete temperature, this will also reduce the modulus of elasticity, reduce the coefficient of thermal expansion, and reduce or eliminate autogenous shrinkage effects, all of which contribute to increasing resistance to early-age cracking.

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Key Findings

  • Concrete containing increased amounts of lightweight aggregates experienced higher concrete temperatures compared to the control concrete.
  • The presence of lightweight aggregates delayed the time to cracking.
  • Increasing the amount of lightweight aggregate in the concrete results in a greater reduction in modulus of elasticity, coefficient of thermal expansion, and autogenous shrinkage. These effects all contribute to greater resistance to early-age cracking.

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