Zahra Abdollahnejad

Cost-efficient one-part alkali-activated mortars with low global warming potential for floor heating systems applications

Increasing building energy efficiency is one the most cost-effective ways to reduce emissions. The use of thermal insulation materials mitigates heat loss in buildings, therefore minimising heat energy needs. In recent years, several papers were published on the subject of foam alkali-activated cements with enhanced thermal conductivity. However, on those papers cost analysis was strangely avoided. This paper presents experimental results on one-part alkali-activated cements. It also includes global warming potential assessment and cost analysis. Foam one-part alkali-activated cements cost simulations considering two carbon dioxide social costs scenarios are also included. The results show that one-part alkali-activated cements mixtures based on 26%OPC + 58.3%FA + 8%CS + 7.7%CH and 3.5% hydrogen peroxide constitute a promising cost-efficient (67 euro/m3), thermal insulation solution for floor heating systems. This mixture presents a low global warming potential of 443 KgCO2eq/m3. The results confirm that in both carbon dioxide social cost scenarios the mixture 26 OPC + 58.3 FA + 8 CS + 7.7 CH with 3.5% hydrogen peroxide foaming agent is still the most cost efficient.

Durability performance of fly ash based one-part geopolymer mortars

Environmental concerns regarding the high CO2 emissions related to the production of ordinary Portland cement (OPC) led to research efforts on the development of eco-efficient alternative binders. Geopolymers constitute promising inorganic binders alternative to OPC which are based on aluminosilicates by-products and alkali activators. The geopolymerization technology of aluminosilicates is a complex chemical process evolving dissolution of raw materials, transportation, orientation and polycondensation of the reaction products. Classical two part geopolymers could become more eco-efficient with a lower CO2 footprint if sodium silicate usage is avoided. Besides current geopolymeric mixes can suffer from efflorescence originated by the fact that alkaline or soluble silicates that are added during processing cannot be totally consumed during geopolymerisation. Therefore, new and improved geopolymer mixes are needed. One-part geopolymers (sodium silicate free) were first proposed in 2007. However, very few papers were published on these materials. This paper presents experimental results on the durability performance of one-part geopolymers concerning water absorption, penetration of chloride, carbonation resistance and resistance to acid attack. Hydration products results assessed by FTIR spectra are also presented.

Compressive strength, microstructure and hydration products of hybrid alkaline cements

Ordinary Portland cement (OPC) is the dominant binder in the construction industry with a global production that currently reaches a total of 3 Gt per year. As a consequence, the cement industrys contribution to the total worldwide CO2 emissions is of about 7% of the total emissions. Publications on the field of alkali-activated binders (also termed geopolymers), state that this new material is, potentially, likely to fbecome an alternative to Portland cement. However, recent LCA studies show that the environmental performance of alkali-activated binders depends, to great extent, of their composition. Also, researchers report that these binders can be produced in a more eco-efficient manner if the use of sodium silicate is avoided. This is due to the fact that the referred component is associated to a high carbon footprint. Besides, most alkali-activated cements suffer from severe efflorescence, a reaction originated by the fact that the alkaline and/or soluble silicates that are added during processing cannot be totally consumed. This paper presents experimental results on hybrid alkaline cements. The compressive strength results and the efflorescence observations show that some of the new mixes already exhibit a promising performance.

Comparative Study on the Effects of Recycled Glass–Fiber on Drying Shrinkage Rate and Mechanical Properties of the Self-Compacting Mortar and Fly Ash–Slag Geopolymer Mortar

AbstractIn this comprehensive experimental study, the effects of recycled glass fiber on the drying shrinkage and mechanical properties of the self-compacting mortar and fly ash–slag geopolymer mor...

Cost efficiency and resistance to chemical attack of a fly ash geopolymeric mortar versus epoxy resin and acrylic paint coatings

This article presents results of an experimental investigation on the resistance to chemical attack (with sulphuric, hydrochloric and nitric acid) of several materials: OPC concrete, high-performance concrete, epoxy resin, acrylic painting and a fly ash-based geopolymeric mortar). Three types of acids with three high concentrations (10, 20 and 30%) were used to simulate long-term degradation. A cost analysis was also performed. The results show that the epoxy resin has the best resistance to chemical attack independently of the acid type and the acid concentration. However, the cost analysis shows that the epoxy resin-based solution is the least cost-efficient solution being 70% above the cost efficiency of the fly ash-based geopolymeric mortar.

Development of deflection hardening cementitious composites using glass fibres for flexural repairing/strengthening concrete beams: experimental and numerical studies

Abstract This paper presents experimental and numerical programmes employed to strengthen concrete beams using glass fibre-reinforced concrete in order to achieve deflection hardening behaviour. Numerous tests were carried out on 270 specimens in the experimental phase in order to characterise mechanical properties of beams reinforced with glass fibre. Three beams were then cast with plain concrete and experimentally tested under flexural load conditions. Based on the experimental results, numerical simulations were conducted and the results were calibrated to the experimental results. Then, the robust-able FE models were used to strengthen concrete beams through numerical simulations. Furthermore, section enlargement method was also used to strengthen the concrete beams. The experimental and numerical results showed that using glass fibre-reinforced concrete layer to strengthen the concrete beams through the section enlargement method significantly improves the load carrying capacity and ultimate deflection.

Short-term compressive strength of fly ash and waste glass alkali-activated cement based binder (AACB) mortars with two biopolymers

AbstractThe Roadmap to a Resource Efficient Europe aims that by 2020, waste will be managed as a resource. Thus materials that have the ability for the reuse of several types of wastes, such as alk...

The suitability of concrete using recycled aggregates (RAs) for high-performance concrete (HPC)

Most studies related to concrete made with recycled aggregates (RA) use uncontaminated aggregates produced in the laboratory, revealing the potential to re-use as much as 100%. However, industrially produced RA contain a certain level of impurities that can be deleterious for Portland cement concrete, thus making it difficult for the concrete industry to use such investigations unless uncontaminated RA are used. This chapter reviews current knowledge on concrete made with RA, with a focus on the crucial importance of the presence of impurities, and how those aggregates are not suitable for the production of high-performance concrete (HPC). The potential of geopolymers to produce HPC based on high volume RA is also discussed.

Performance of a Fly Ash Geopolymeric Based Binder with Calcium Hydroxide, Portland Cement and Metakaolin as Additives

Funding: This study was funded by Foundation for Science and Technology (FCT) in the frame of project IF/00706/2014-UM.2.15.

Carbon dioxide sequestration of fly ash alkaline-based mortars containing recycled aggregates and reinforced by hemp fibers: Properties, freeze-thaw resistance, and carbon footprint

The authors would like to acknowledge the financial support of the Foundation for Science and Technology (FCT) in the frame of project IF/00706/2014-UM.2.15.