Residual Cementing Property in Recycled Fines and Coarse Aggregates: Occurrence and Quantification

Abstract

The adhered cement mortar in coarse aggregates and fines from demolished concrete has the potential to induce a residual cementing property upon recycling. A procedure for quantifying the contribution of recycled fines to the strength gain within the new mortar matrix is proposed. The strength gain is found to be more significant in recycled aggregates and fines from brick aggregate concrete than in those from stone aggregate concrete. Isothermal calorimetry measurements indicate the existence of large heat flows immediately after wetting and a prolonged initial reaction period during the hydration of recycled fines due to the presence of unreacted cement compound fractions and depleted amounts of gypsum. This phenomenon has been further confirmed, particularly in recycled fines from brick aggregate concrete, through electron microscopy observations of the formation of new gel structures due to rehydration. The chemical compositions determined using two independent methods indicated possible interactions between CH (the hydration product) and pozzolan (from brick) to induce strength gain in new mortars and new concrete obtained by recycling brick aggregate concrete. This explanation is consistent with the strength test results and the evolution of the heat events observed calorimetrically.

Concrete Grinding Residue: Management Practices and Reuse for Soil Stabilization

“…Soil with the higher specific area can also benefit more in relation to strength improvement because of Ca 2+ absorption on soil particles and this can explain why CGR is more effective in improving the strength of finer soils (Soil 2). Long-term strength improvement was also observed in CGR-treated specimens, and hydration and rehydration of cementitious materials and unreacted cement in CGR were hypothesized to be the contributor ( 60 ). Pozzolanic reactions between Ca, Si, and Al (calcium silicate hydrate [C-S-H] and calcium aluminum hydrate [C-A-H]) may be another contributor to achieving long-term strength.…”

“…Goodwin and Roshek ( 4 ) concluded that recycling of CGR as a filler in cement-treated base resulted in lower construction cost with a similar mechanical performance compared with the traditional industrial treatments such as processing in waste facilities. Amin et al ( 60 ) investigated the reuse of recycled concrete fines for strength gain within a cement mortar matrix and showed that rehydration was observed in the mortar, which resulted in strength gain. On the other hand, Kluge et al ( 9 ) examined the CGR for potential use as a partial replacement of cement in new concrete and found no dramatic reactivity or improvement in mortar strength.…”

Quantification of Residual Unhydrated Cement Content in Cement Pastes as a Potential for Recovery

“…Several studies investigated the possibility of rehydrating the decomposed hydrated cement paste fines after thermal treatment [14,[16][17][18]. Another category of studies investigated the cementing contribution of hydrated cement paste fines through cement replacement, with no further treatment [19][20][21][22]. In these studies, new mortar/cement paste was produced, in which cement was replaced, at different replacement rates, by recycled fines from crushing and grinding of concrete/cement paste.…”

“…In these studies, new mortar/cement paste was produced, in which cement was replaced, at different replacement rates, by recycled fines from crushing and grinding of concrete/cement paste. For comparison, in [19], limestone filler was used to replace cement, while in [21], natural fine sand was used as an inert replacement. All studies found a progressive decrease in strength with the increase in the replacement rate of cement by said fine materials [19][20][21].…”

Characterisation and management of concrete grinding residuals

“…The physical and chemical composition of CGR is similar to Portland cement, which makes it a candidate for several beneficial use applications. Previous research has suggested that CGR will contain partially unreacted cement and may thus exhibit some cementing properties when reused (Amin et al, 2016; Connolly et al, 2010). The presence of calcium, potassium, magnesium, and sodium salts in the chemical makeup of CGR may also have some benefits to plant growth if used as a soil amendment (DeSutter et al, 2011; Mamo et al, 2015), as well as an ability to neutralise acidic conditions (Scott, 1985).…”