Waste glass is considered for use in a geopolymer binder systems based on the high Si content, amorphous framework structure, adequate hardness and widespread availability. A lack of Al within the system, however, must be taken into account, as Si/Al and Na/Al ratios have been shown to affect properties such as setting time, compressive strength and microstructure. Metakaolin and fly ash were added to a glass-based system, lowering the Si/Al and bringing Na/Al closer to unity. Mortars made using 100% glass as well as 25 and 50% of fly ash or metakaolin by mass were activated with 10M NaOH and cured at 80°C for 24 hours. Microstructural characterization of fracture surfaces and thin sections as well as compressive strength and degree of reaction data was collected. The 100% glass mixture (Si/Al – 8.39, Na/Al – 1.61) and 25% metakaolin (Si/Al – 4.96, Na/Al – 0.97) mixtures showed a dense, continuous microstructure. The 25% MK mix resulted in a 1-day f’c of above 5000 psi (35 MPa), while the 50% metakaolin mixture (Si/Al = 3.45, Na/Al – 0.69) developed little strength and had a low-density microstructure, possibly due to the high water demand. Mixtures containing fly ash resulted in reasonable compressive strengths and moderately dense microstructures.

Compared to the hydration process of traditional Portland cements, phosphate-based cements rely on an acid/base reaction process to quickly achieve strong, lightweight and durable binders with lower embodied energy. Since the binding action relies on the chemical composition of the initial components, the rheological and mechanical properties of the resulting ceramic concretes can also be influenced by other mix components including fly ash, fillers and aggregates. This paper reports on an ongoing study examining properties of concretes produced with magnesium potassium phosphate cement binders that incorporate fly ash contents of up to 80% of the total binder mass. Highly flowable mixes were developed with setting times that could be controlled through use of commonly available admixtures. The highest compressive strength of the binders and mortars were achieved when the fly ash content was 50% of the total binder mass. The produced binders and sand mortars had densities of 1800 kg/m3 [3034 lb/yd3] and 2100 kg/m3 [3540 lb/yd3] and compressive strengths of 35 MPa [5.0 ksi] and 60 MPa [8.7 ksi] after 28 days of simple ambient curing. Decreases in both strength and density were observed as the fly ash content was increased further, but remained within practical ranges for common construction applications with high fly ash contents.

One of the primary approaches to producing more sustainable concretes consists of replacing 50 % or more of the portland cement in a conventional concrete with fly ash, producing a so-called high volume fly ash (HVFA) concrete. While these mixtures typically perform admirably in the long term, they sometimes suffer from early-age performance issues including binder/admixture incompatibilities, delayed setting times, low early-age strengths, and a heightened sensitivity to curing conditions. Recent investigations have indicated that the replacement of a portion of the fly ash in these concrete mixtures by a suitably fine limestone powder can mitigate these early-age problems. The current study investigates the production of concrete mixtures where either 40 % or 60 % of the portland cement is replaced by fly ash (Class C or Class F) and limestone powder, on a volumetric basis. The mixtures are characterized based on measurement of their fresh properties, heat release, setting times, strength development, rapid chloride penetrability metrics and surface resistivity. The limestone powder not only accelerates the early age reactions of the cement and fly ash, but also provides significant benefits at ages of 28 d and beyond for both mechanical and transport properties.

The fly ash based hydraulic binder (FAHB) described in this paper is comprised of ASTM Class C fly ash, ASTM class F fly ash and two proprietary non-caustic liquid activators. FAHB, a zero carbon footprint binder, is successfully used in making Green Concrete (eGC.) The eGC neither needs wet curing like Portland cement Concrete (PCC) nor needs elevated curing temperature like geopolymer cement concrete. The water demand of eGC is much lower than the water demand of PCC. Though, eGC follows Abrahms’ water-to-cement ratio (W/C) law, it has different sets of curves to estimate the W/C from the required 28-day compressive strength of concrete (f’cr). A little different approach is needed for proportioning the eGC using FAHB. This paper presents the model for estimating the water demand of eGC, the approximate relation between the W/C and f’cr and the step- by- step guideline for mix proportioning of eGC using FAHB, a carbon neutral binder system consisting of no Portlannd cement. The mixture proportioning method proposed in this paper will help concrete engineers and ready mixed concrete producers in designing cost effective and durable eGC. This method permits users to design eGC for wide range of workability and compressive strength.

Over the last few decades there has been an increasing interest in low-carbon-foot-print binders that can replace hydraulic cement in concrete mixtures. Given that hydraulic cement is so ingrained in the building materials industry, alternative binders –in addition to offering a low carbon footprint– must exhibit similar or improved consistency and properties in a cost effective manner. A candidate that meets these criteria is activated high-calcium fly ash (AHCFA), which as the name implies uses high-calcium fly ash (HCFA) as main reactive powder along with an activator to increase its hydraulic activity and a setting retarder to regulate the rate of reaction. It is an attempt to get a better understanding of the factors that have greater influence in the reactivity of HCFA. The physical, chemical and crystallographic characterization as well as glass fragility analyses of several HCFA samples was paralleled with the compressive strength of their corresponding AHCFA mortars. Correlations between HCFA characteristics and the compressive strength of the resulting AHCFA mortars were sought. The results suggest that the reactivity of HCFA can be evaluated in terms of glass fragility using non-bridging oxygens per tetrahedron (NBO/T) and alumina saturation index (ASI) as main parameters.