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.

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.

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.

There is a growing interest all over the world to develop and implement environmentally friendly binding materials for concrete applications. The emphasis of the research and construction community is on finding sustainable alternatives for ordinary portland cement to reduce the overall environmental and energetic impact of cement production. The use of high volumes of fly ash and slag are already accepted means of cement reduction for sustainable concretes; however, the dramatic increase in the consumption of concrete requires novel and sustainable binder systems. Recent research results is to provide an introduction into several areas of active work on green binder systems. The papers in this CD deal with a wide variety of topics that are of significant interest and impact, including the chemistry of geopolymerization of fly ash, mixture proportioning of concretes containing fly ash alone as the binder, methods to improve the reactivity of fly ash through nanomodification or the use of fine limestone, and phosphate-based cements. Also, novel methods of the use of waste glass powder and rice husk ash as cementing materials are detailed. These paper are a useful addition to the library for any researcher, materials producer, or end user interested in alternative and sustainable binding materials for concrete. This CD consists of 8 papers that were presented at a technical session sponsored by ACI Committees 130. 232, and 236 at the ACI Convention in Dallas, TX, in March 2012. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-294

Rice husk ash can be used as a supplementary cementing material. It is a waste material from the burning of rice husks for energy. Rice husk ash contains a mesoporous morphology of silica and this morphology has high hydrophilic properties. When rice husk ash is used in concrete mixtures, the flowability of the mixtures decreases. This makes the acceptance of rice husk ash in the concrete industry more challenging. Reduced workability hinders the potential use of rice husk ash in the field. Some research has investigated the potential use of using mechanical grinding (e.g., ball mill) to reduce particle size of rice husk ash with the hopes of improving the workability of concrete containing RHA, but this method requires significant energy and results in high wear of the equipment. The work investigates the use of a chemical treatment process of rice husk ash. This chemical treatment process reduces the particle size and breaks down the mesoporous morphology, thereby improving the fresh characteristics of concrete containing RHA and decreasing its water requirements. Because changes in setting behavior and reduced early-age strength development are other concerns when using some supplementary cementing materials, this work also investigates the setting, early-age compressive strength development, and porosity of cementing material systems containing 10% and 15% RHA replacements.