Page 27 - New Trends in Green Construction

INFLUENCE OF DIFFERENT CHEMICAL ADMIXTURES ON CEMENT BASE MORTAR PROPERTIES
Ana Isabel Torres Gómez, Enrique Fernández-Ledesma, José María Fernández, José Ramón Jiménez
Keywords: recycled aggregates, admixtures, plasticizer, superplasticizer, mortar 1. Introduction
The use of the fine fraction of construction and demolition waste (CDW) is a viable alternative for masonry mortar production. Ledesma et al. (2015) concluded that it is possible to replace up to 50% of natural sand with recycled sand from CDW without affecting the mechanical properties in a significant manner. Workability, shrinkage and freeze-thaw resistance are the most limiting properties; hence we recommend the use of recycled sand from CDW only for masonry mortar production in indoor environments.
Currently, there are different types of chemical admixtures in the market for mortar and concrete that allow to improve properties such as workability, the time of setting, mechanical strength and durability.
The objective of this work was to study the effect of different types of commercial admixtures on the properties of cement-based mortars made with natural and recycled aggregates from CDW.
2. Material and methods
Two 0/4 mm sands were used: a natural siliceous sand (AN) as a reference and the fine fraction (recycled sand) from a mixed recycled aggregate whose components according to UNE-EN 933- 11: 2009 were: concrete and mortar (38.24%); unbound natural aggregates (31.47%); ceramic materials (28.85%); bituminous materials (1.14%); gypsum (0.15%); 0.01% glass and others like wood, plastic, etc. (0.4%). A cement CEMIV / B (V) 32.5 N was used. Four types of admixtures were tested: an air entrainers & plasticizers (Mastercast 934), an air entrainers & water retainer (Mastercast 930), a set retarding & plasticizers (Mastercast 560) and a superplasticizers & water reducer (Mastercast 205 MA).
Table 1 shows the mortar mix proportions. The amount of water was adjusted experimentally until achieving a consistency of 175 ± 10 mm (EN 1015-3: 1999). Aggregates were used at room temperature (20 °C) and humidity. The recycled sand moisture was around 2.68% while the natural sand moisture was around 0.2%.
The following properties were studied: workability (UNE-EN 1015-9: 2000), compression strength (UNE-EN 1015-11: 1999) at 28 and 180 days and shrinkage (UNE 83831: 2010) at 28 days.
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New Trends in Green Construction