Impact of recycled sand and gravels in concrete on volume change

Abstract

The nature and the porosity of sand and gravel impact significantly the development of the free deformation at early age of cement based materials. For recycled concrete, the high porosity and the subsequent internal water curing provided by recycled sand and gravels cause a decrease of the autogenous shrinkage, limit the increase of the CTE during the first days after setting and globally increase the CTE (up to 50%). A new model was developed for the consideration of the internal curing effect on the development of the autogenous strain. It is observed that the autogenous strain development induced by the internal water curing effect of the recycled sand and gravels can be modelled by an exponential law according to the equivalent age and by a sinusoid law according to the hydration degree.

Advanced techniques for the study of shrinkage-induced cracking of concrete with recycled aggregates at early age

“…The development of the free strain can be divided in three stages. The first stage shows a rapid increase of the shrinkage with a magnitude of 20-30 mm/m and takes place between the final setting and an age of around 20 h. During this period, the development of the free strain is mainly driven by the self-desiccation of the cement paste [16]. The presence of recycled gravel and sand decreases slightly the shrinkage magnitude.…”

“…The absorption coefficient depends on the fraction (fine or coarse) and the origin of recycled aggregates. During the hydration process, recycled aggregate can be considered as a water tank for the cement paste and thus plays the role of an internal curing agent [16]. This phenomenon reduces and/ or delays the decrease of the internal relative humidity of the cement paste [17,18].…”

Influência do efeito fíler do pó de mármore na produção de concretos para pavimentos intertravados

“…O concreto é o segundo material mais utilizado no mundo. Os agregados correspondem de 60% a 75% do volume da mistura de concreto, e a qualidade desses componentes influencia nas características e propriedades do concreto produzido (DELSAUTE; STAQUET, 2020). No Brasil, a demanda por agregados na construção civil em 2021 foi superior a 660 milhões de toneladas, das quais 42% foram de brita e 58% de areia (ASSOCIAÇÃO NACIONAL..., 2022).…”

Development of early age autogenous and thermal strains of alkali-activated slag-fly ash pastes

“…Self-desiccation due to the water-consuming reaction leads to the formation of water-air menisci, and the internal relative humidity decreases, which induces a capillary depression of the pore fluid (Serdar et al, 2020). While the former two mechanisms lead to shrinkage, swelling may be caused by absorption of external water (Bjøntegaard et al, 2004;Esping, 2008;Craeye et al, 2010), absorption of internal water provided by water-releasing porous aggregates (such as light-weight or recycled aggregates; Delsaute and Staquet, 2019;Bendimerad et al, 2020;Delsaute and Staquet, 2020), or by the expansion pressure during the formation of reaction products such as ettringite (Mehta, 1973;Bentur and Ish-Shalom, 1974).…”