Geomechanical Behaviour of Recycled Construction and Demolition Waste Submitted to Accelerated Wear

The construction industry is one of the most important sectors for economic and social development. However, it is responsible for more than 50% of the depletion of natural resources, for 40% of the energy consumption and construction and demolition waste (CDW) accounting for 30-60% of the total municipal solid waste generated worldwide. In this sense, the recycling of CDW is considered a safe alternative to the current trend, which can produce environmental and economic benefits, namely the reduction of the depletion of natural resources and the volume of waste sent to landfills. Some studies have shown promising results in the use of recycled CDW as geotechnical materials. However, the degradation performance induced by the construction procedures and weather conditions on the geotechnical behaviour of recycled CDW is still a research gap, creating an obstacle for its regular use in general engineering practice. This work evaluated the mechanical performance of recycled CDW over time when subjected to wetting-drying degradation cycles under different temperature and pH conditions. The effects of such degradation were then evaluated qualitatively (changes in particle size distribution and Proctor parameters) and quantitatively (stress-strain response and permeability). The results showed that 10 wetting-drying cycles and different compaction energies have no change in the particle size distribution of CDW compared to the original CDW. The shear strength parameters were very similar for the different degradation conditions except when different pH values were used, which may have weakened the grains and decrease the friction angle of the material. Regarding the permeability, all tested samples were classified in the same hydraulic conductivity range (very low) without significant changes induced by the degradation mechanisms

Sustainable alkali binders: Waste activating wastes

Alkaline binders usually requires two main components, namely the solid precursor, rich in alumina and silica (preferably in an amorphous state); and the activator solution, based on an alkali metal (usually sodium or potassium). The role of the precursor is commonly assumed by a residue, usually fly ash or blast furnace slag with significant economic and environmental benefits. However the activator is frequently prepared with first grade commercial reagents (usually sodium or potassium hydroxide and sodium or potassium silicate), which significantly increases the financial costs and severely dilutes the environmental initial advantages, due to the high CO2-eq released during the production of the reagents. These drawbacks associated with the activator severely hinder the wide spreading of this technology severely making the development of low cost activators a major research target. Therefore, a strong expectation regarding the application of industrial residues as the main (or even the sole) constituent of the activators – and not just as the precursor – is rapidly growing. The aim of the present paper is thus to analyse the potential application of some by-products, in this case from the aluminium foundry industry, as the alkali activator of two different precursors: fly ash type F (FA) and blast furnace slag (BFS)

Estabilización de suelo arcilloso utilizando materiales cementicios activados alcalinamente

In this study, a clayey soil classified as A-7-5 according ASTM D3282, was stabilized using alkali-activated cementitious materials (AAC) added to the soil dry in percentages of 20 and 30%. Fly ash (F1, F2) with high unburned carbon content (up to 38.76%), hydrated lime (L) and granulated blast furnace slag were used. Unconfined compressive strength and flexural strength at 28 days of curing and the durability after 12 wetting-drying cycles were evaluated. The results were compared with a soil-cement reference mixture. The soil treated with AAC-F1L showed a volume expansion of 0.51% and volume contraction of -0.57% compared with the 0.59% expansion and -0.68% contraction of the soil-cement reference mixture. Additionally, the mass loss after the wetting and drying cycles is only 3.74% which is slightly lower than the mass loss of the soil stabilized with ordinary Portland cement (OPC) (3.86%) and well below the value specified in Colombian regulations (7%).En este estudio, un suelo arcilloso clasificado como A-7-5 según ASTM D3282, se estabilizó utilizando materiales activados alcalinamente (AAC) en porcentajes de 20 y 30%. Se utilizaron cenizas volantes (F1, F2) con alto contenido de inquemados (hasta 38,76%), cal hidratada (L) y escoria granulada de alto horno. Se evaluó la resistencia a la compresión confinada y la resistencia a la flexión a 28 días de curado y la durabilidad después de 12 ciclos de humectación-secado. Los resultados se compararon con una mezcla de referencia suelo-cemento. El suelo tratado con AAC-F1L mostró una expansión y contracción volumétrica del 0,51% y -0,57% respectivamente, en comparación con el 0,59% y -0,68% de la mezcla de referencia suelo-cemento. Además, la pérdida de masa después de los ciclos de humectación y secado es sólo 3.74%, valor ligeramente inferior a la del suelo estabilizado con cemento Portland (3.86%) y muy inferior al valor especificado en la normativa colombiana (7%)

Improvement of a clayey soil with alkali activated low-calcium fly ash for transport infrastructures applications

The improvement of geotechnical properties is often achieved by the addition of traditional binders, such as cement or lime. However, the use of such binders implies a considerable financial and environmental cost that needs to be mitigated. An unconventional solution, similar to cement in terms of performance but more environmentally friendly, consists in the use of binders made from alkaline activated industrial residues. The technique consists on the activation of raw materials (such as fly ash or blast furnace slag) rich in Si, Al, or even Ca, with high pH alkaline solutions. The present work was developed aiming the possible stabilisation, using different fly ash contents, of a clayey soil with sand. The activator solution was composed of sodium hydroxide and sodium silicate. The extended experimental campaign included unconfined compressive strength (UCS), California Bearing Ratio (CBR), pulse velocity tests and triaxial tests to assess the geomechanical improvement induced by the new binder. As a mean of comparison, the experimental campaign included also the stabilisation of the same soil with either cement or lime. The obtained data indicates that the use of alkaline activation as a soil stabilisation technique provides competitive geomechanical results, when compared with those obtained with traditional binders.(undefined

Alkali-Activated Fly Ashes: Influence of Curing Conditions on Mechanical Strength

Alkaline activation of fly ashes is a procedure that enables an alternative binder which has been receiving much interest by several research groups particularly on the manufacturing of mortars and concretes. The properties of the materials that are developed during the alkaline activation are influenced by the curing conditions (temperature and relative humidity). Another relevant facet related to the curing procedures is the possibility of carbonation occur, which may have an impact on the mechanical strength of the alkaline cements. In this research, several sets of curing conditions were tested to understand which one results in a higher strength and reveals carbonation. Uniaxial compressive strength tests were conducted to assess mechanical behavior. The outcome suggests that higher temperature and low relative humidity yields higher mechanical strength

Increasing the reaction kinetics of alkali-activated fly ash binders for stabilisation of a silty sand pavement sub-base

The paper addresses several options to improve the reaction kinetics of alkali-activated low-calcium fly ash binders for soil stabilisation in road platforms. For that purpose, an experimental programme was established to assess the strength evolution, with time, of different binders, based on ash, lime, sodium chloride and alkali solutions, applied in the stabilisation of a silty sand. The tests included unconfined compression strength tests, triaxial tests and seismic wave measurements performed at different curing periods. The results were compared with a binder made of Portland cement and a commercial additive specifically designed for soil stabilisation in road applications. The activated ash mixtures with lime were the most performing producing a significant increase in the reactions development and, consequently, in the strength gain rate. The sodium chloride significantly improved the lime and lime-ash mixtures, but provided only a slight improvement in the activated ash mixtures.The authors would like to acknowledge the company CJR Wind – Energy for life, for the funding which enable the presented research; the MCTES/FCT (Portuguese Science and Technology Foundation of Portuguese Ministry of Science and Technology) for their financial support through the SFRH/BPD/85863/2012 scholarship, which is co-funded by the European Social Fund by POCH program; and the Microscopy Unit of the University of Trás- os-Montes e Alto Douro. In addition, a special acknowledgment is also due to PEGOP – Energy Eléctrica, S.A. and LUSICAL – Companhia Lusitana de Cal, S.A. for providing respectively fly ash and lime for this study

Influence of grain size and mineralogy on the porosity/cement ratio

The porosity/cement ratio is defined as the ratio between porosity and the volumetric cement content (volume of cement over the total volume) and it is often adjusted by an exponent (xi) to the volumetric cement content (n/C-iv(xi)), which seems to depend on the type of soil. This ratio is very useful to analyse artificially cemented soils and it depends on easily calculated moulding properties. Although there are already some results regarding the correlation of this ratio with the mechanical behaviour of different soils, a theory explaining the variation of the exponent xi has yet to be established. In this work, the influence of grain size and mineralogy on xi was pursued, considering them to be the most important factors. For that purpose, a soil was divided into three different fractions, whose grain size distribution and mineralogy were known, and the exponents obtained correlating the ratio with the maximum shear modulus or the unconfined compression strength were compared. The results show that the grain size distribution explains part of the xi variation, but mineralogy and particle shape seem to have the most decisive influence. This was even more evident when comparing two uniform sands

Tensile strain hardening of a metakaolin based fibre reinforced composite

Portland cement concrete is the most used building material in the world. However, its manufacture is energy-intensive and it is susceptible to harsh environments. Alternative binder systems without ordinary Portland cement, such as geopolymers or alkali-activated materials, are recently new in the Civil Engineered world. These alternative binder systems seek, among other characteristics, improved durability and environmental efficiency. The attaining of strain hardening and multiple cracking typical of Strain Hardening Cementitious Composites (SHCC) using these alternative binder systems is very attractive from a conceptual point of view, since additional endurance to certain harsh or extreme environments, as well as enhanced durability, are usually expected as two of the main outcomes. In the present work, the behaviour of two different composites was studied: an existing Engineered Cementitious Composite (ECC) and a new composite based on an alternative binder prepared with metakaolin. Polyvinyl alcohol (PVA) fibres were used in both materials. A series of experiments, including compressive and direct tensile testing were carried out to characterize and compare the mechanical properties of both materials. The results showed that the alternative binder composite, when subjected to uniaxial tension, developed multiple cracks at steadily increasing tensile stress and strain, which is also typical of ECCs showing strain hardening behaviour. The development of fibre reinforced geopolymer or alkali-activated materials showing strain hardening ability in tension may still be considered as a novel research topic, with great potential for creating new and interesting developments for Civil Engineering and structural applications, particularly the ones subjected to harsh environments

Sustainability assessment of half-sandwich panels based on alkali-activated ceramic/slag wastes cement versus conventional building solutions

This study assessed the sustainability of two partition walls and intended to contribute to the Circular Economy in the construction sector. A life cycle approach and a multi-criteria decision support method were applied to know the environmental, functional, and economic performances of the production process of half-sandwich panels based on alkali-activated ceramic/slag waste cement, choosing as system boundary the method “cradle to gate”. The proposed building solutions differ from each other in the type of insulating material used, either extruded polystyrene foam (APXPS) or expanded cork agglomerate board (APICB). Besides, a comparative analysis of the developed building solutions versus three reference constructive solutions: i) a conventional heavyweight partition wall, ii) a lightweight gypsum wall panel, and iii) a conceptual lightweight sandwich membrane building solution was performed. Results showed that the two proposed half-sandwich wall panels (APXPS and APICB) resulted in the most sustainable alternatives, of which the APXPS obtained the best overall results since it combined the best environmental, functional, and economic behavior. Besides, the environmental contribution analysis determined that the greatest environmental burden to the Global Warming Potential (GWP), in the case of the APXPS was associated with the XPS (57%), being the alkali activator (23%) placed as the second major contributor. When the ICB was used as the insulation layer, the energy used (nearly 38%) and the sodium silicate (about 17%) were the larger contributors to CO2 emissions. It is worth mentioning that the use of ICB represented a negative contribution (of about −34%) to the GWP category.This work was partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/ 04029/2020, and the research project “CirMat: CIRcular aggregates for sustainable road and building MATerials”(ref. 16_Call#2)is funded by Iceland, Liechtenstein and Norway through the EEA Grants and Norway Grants, operationalized by the Portuguese Office of the Secretary of State for the Environment. RENEw, POCI-01-0247-FEDER-033834, that was co-funded by Fundo Europeu de Desenvolvimento Regional (FEDER), with Programa Operacional da Competitividade e Internacionalizaçao ˜ do Portugal 2020 (COMPETE 2020) The authors acknowledge the support of the DST group construction company for funding the project Chair DST/IB-S: Smart Systems for Construction