Mechanical, durability and economic performance of concrete incorporating fly ash and recycled aggregates

Abstract

This paper studies the impact of replacing natural coarse aggregates (NCA) with recycled coarse aggregates (RCA) and cement (OPC) with fly ash (FA), on properties and economy of concrete. RCA was obtained by crushing old concrete specimens. FA of low calcium type was used to partially replace OPC. A total of nine concrete mixes (including a reference mix) were prepared using 50% RCA, and 100% RCA with four different levels of FA (0% FA, 10% FA, 20% FA, 30% FA). Workability, fresh density, compressive strength, apparent porosity, and bulk density was measured to evaluate the performance of each mixture. Mixes with optimum levels of both RCA and FA reaching the compressive strength potential of reference mix at 90 days, were subjected to chloride migration testing. To ascertain the combined impact of RCA and FA on economic and strength performance of concrete, a cost to strength ratio (CSR) analysis was also performed on all mixes. Results of testing indicate that FA compensates the loss in workability of fresh concrete and improve the compressive strength of RCA concrete at 28 and 90 days. Negative influence of RCA on density and porosity is minimized by consumption of FA in concrete. Mixes with 50% RCA and 20-30% FA show better resistance against chloride penetration compared to that of the reference mix. CSR analysis suggests that FA must be used along with RCA in concrete in order to minimize the negative influence of RCA on both cost and strength.

Evaluation of Mechanical and Permeability Characteristics of Microfiber-Reinforced Recycled Aggregate Concrete with Different Potential Waste Mineral Admixtures

“…has been studied widely considering the mechanical performance of the material. FA also improves the workability of RAC and reduces the requirement of water-reducing chemicals to attain the required level of flow in fresh concrete [16]. Poon et al [17] reported that the drawbacks of RAC (such as poor durability) can be minimized by the utilization of 25-35% FA as a cement substitution material.…”

Enhancing the Hardened Properties of Recycled Concrete (RC) through Synergistic Incorporation of Fiber Reinforcement and Silica Fume

“…It is well understood that, despite environmental and economic benefits [6,7], RC has inferior hardened properties compared to natural/normal aggregate concrete (NC). RA containing the low-density mortar is the weakest link in RC.…”

Concreto de baja permeabilidad para pilotes prefabricados de muelles construidos en zonas de salpicaduras y mareas utilizando nanotubos de carbono de pared múltiple

“…En las tablas VII, VIII y IX se muestran los análisis de precios unitarios para la elaboración de 1 m 3 de tres tipos de concretos: NTC-0, NTC-0.15 y con cenizas volantes para un 30% de adición (CV-30), habiéndose escogido la CV por sus propiedades puzolánicas similares al NTC. Para los dos primeros, los precios unitarios se obtuvieron de [33] y en el NTC-0.15 se incluyó el transporte de 1 Kg de NTC desde Nanjing-China a Lima-Perú por el importe de $49.92 USD; y para el tercero los precios se obtuvieron de [34]. En las Tablas mencionadas se observa que los costos unitarios totales para 1 m 3 [35], realiza el estudio del asentamiento de dos mezclas de concreto con NTC y una mezcla de concreto convencional (0%), empleando las cantidades de 0.3% de adición de NTC con dispersión y 0.3% sin dispersión.…”

“…Son escasas las investigaciones en el campo económico sobre la utilización de los NTC en la fabricación del concreto, la Ref. [34] estudia el reemplazo del cemento por cenizas volantes (CV) y por NTC, para evaluar su costo/resistencia con respecto al NTC-0; encontrando que con 30% de CV se reduce el costo total del concreto en más del 15% y que el concreto con NTC es más caro, ambos, que el concreto con NTC-0.…”