Alkaline activation: Cement mortars and recycled brick dust

Abstract

In the present research work, the percentage of replacement by weight of recycled brick dust (PLR) in portland cement mortars (CP) was evaluated; replacement percentages were 20% , 40%, 60%, 80%, and 100%, respectively. The PLR was activated alkaline, for which a solution of NaOH (2M) and sodium silicate (3M) (30/70) v/v was used; the PLR was obtained from the selection and grinding of construction debris from the district of Víctor Larco Herrera (Trujillo-Peru); the PLR that was used in the mixtures was ground and sieved through a Nº400 mesh (only the passing powder was used). Once the PLR was obtained, the process of preparing mortar samples for compression tests (ASTM C-109) was carried out, according to the aforementioned replacement percentages. The ratio of aggregate (coarse sand) to binder (CP-PLR) was 3:1; the alkaline solution mixture used was included in the kneading water; the water/cement ratio used was 0.55, these three criteria were kept constant in all cases. After demolding and coding the mortars obtained (PLR and CP), they were cured in an electric oven (70 °C /72 hours) and then allowed to cure at room temperature for 28 days; the total curing time (28 days) was also applied to the PLR-free mortars. The compression tested samples were used to determine the percentage of water adsorption (ASTM C 642). The results of the compression test of the L-20 mortars (CP 80% , PLR 20% and the alkaline solution), produced the highest average compressive strength values (18.69 MPa); this value represents an increase of 59.74% , with respect to the PLR-free cement mortars (11.70 MPa, on average), in the same way the same mortar L-20, obtained an average percentage of water absorption of 8.43% , being 10.92% for the PLR-free cement mortar, which represents a decrease in the percentage of water absorption of 22.80%; The differences in the properties evaluated would be due to the formation of additional gels (CSH and CASH) to the typical process of hydration of the cement mortar, which reduce the voids typical of the cement mixtures and therefore increase the density of the mixture, generating the increase in compressive strength and the decrease in the percentage of water absorption. The results are corroborated through the use of XRD characterization techniques; FTIR -ATR, SEM, plus ANOVA statistical evaluation.