Abstract
This research shows the obtaining and characterization of an Alkali Activated Binary Concrete (AABC), based on 70% of a natural volcanic pozzolan (NP) and 30% ground blast furnace slag (GBFS), as a real and environmentally sustainable alternative of replacement to the Portland cement (OPC)-based concrete. As the alkaline activator a mixture of sodium hydroxide and silicate was used. The alkaline binder was characterized prior to the design of the concrete, this included the determination of its compressive strength, setting time and heat of reaction. The mix design of the AABC was performed by adapting the absolute volume methodology used for conventional concretes. AABC was compared equivalently with a concrete based on OPC. The characterization of concretes included the determination of properties such as: slump, compressive strength, density and porosity. In addition, the carbon footprint of the concretes was determined by analysing its life cycle using the LCA methodology. These results are considered as a contribution to the standardization of a real-scale production process of alkaline pre-mixed concretes in countries with deposits of NP such as Colombia.
Highlights
Alkali-activated cements are binders that result from the chemical interaction between strongly alkaline solutions and silicoaluminates, with low and high calcium contents, which may be of natural origin, such as natural clays or pozzolans, or of artificial origin, such as industrial waste and by-products [1]–[5].Alkali-activated concretes are considered to be revolutionary materials that in the foreseeable future could replace in some applications to the Portland cement (OPC)-based concrete ; this idea is supported on its lower carbon footprint and, in general, on the excellent mechanical and durable performances that these have demonstrated since its appearance [6]–[8]
The results allow the classification of activated binder (AAB) as a UG-type cement with a strength of 37.24 MPa, a value that exceeds that required by ASTM C1157 (24 MPa) at 28 days by 55%
In relation to the total heat of reaction of an OPC paste (190 J/g of cementant), the AAB generates 76% less reaction heat, indicating that according to the ASTM C1157, this alternative binder can be classified as a lowheat of reaction cement (LH type), a characteristic that is considered of paramount importance in the construction of massive elements
Summary
Alkali-activated cements are binders that result from the chemical interaction (at relatively low processing temperatures: 25-100°C) between strongly alkaline solutions (activator) and silicoaluminates (precursor), with low and high calcium contents, which may be of natural origin, such as natural clays or pozzolans, or of artificial origin, such as industrial waste and by-products [1]–[5].Alkali-activated concretes are considered to be revolutionary materials that in the foreseeable future could replace in some applications to the Portland cement (OPC)-based concrete ; this idea is supported on its lower carbon footprint and, in general, on the excellent mechanical and durable performances that these have demonstrated since its appearance [6]–[8]. The lack of standards of alkali-activated materials, makes it difficult to produce these materials on an industrial scale from FA and GBFS [13], [14] In this sense, local natural volcanic pozzolans (NP) deposits are considered a viable commercial alternative (industrial scale) due to their greater availability and chemical and mineralogical homogeneity [15], [16]. NP deposits account for approximately 0.84% of the soils worldwide (124 million ha), which are distributed predominantly (60%) in tropical regions [17] These deposits have an important commercial value for the cement industry, especially in countries with high demographic and economic growth, such as: Iran, Cameroon, Japan, China, Saudi Arabia, Turkey, Jordan, USA, Mexico, Chile, Ecuador and Colombia [18], [19]
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