A short review on alkali-activated binders and geopolymer binders

In the recent years, the trend for reusing waste products or industrial by-products to reduce the amount of Ordinary Portland Cement (OPC) in concrete constructions has become an important task for industries and research institutions. OPC is the second most used material in the world after water and statistics confirm that the life cycle of OPC contributes to the generation of up to 5% of the annual CO2 emissions worldwide. Mostly responsible for this negative environmental performance of OPC are the high CO2 emissions related to the cement production processes, namely the deacidification of limestone and the burning of the clinker raw materials at high temperatures above 1400°C. The current demand for cementitious binder is higher than ever whereas the incentive of building sustainable and robust constructions is gaining increasingly in importance. There is a need for development of new more durable and environmental friendly binders as an alternative to OPC binders. Therefore, the research on cement alternatives has risen over the last decades and a lot of research work has been carried out to fulfil the requirements of the market. In this work, the concepts of alkali activated materials and geopolymers are presented, and their properties are compared and discussed. A short historical review is given. Furthermore, the reaction mechanisms and hydration products of these binders are characterized and explained by referring to literature. Finally, novel binders based on waste materials are presented before closing with a short outlook on remaining questions and future challenges

Influence of the sheet profile design on the composite action of slabs made of lightweight woodchip concrete

The trend for using renewable materials in construction to create sustainable and robust buildings is currently gaining in popularity. Therefore, in this work, the applicability of dense lightweight woodchip concrete in constructive engineering is investigated. Here, the material is used as a top concrete layer on composite floors with profiled sheets and is analysed with regard to its load-bearing behaviour and composite action. One specific concrete mixture which fulfils the requirement for minimum strength of LC 20/22 is used for the test series. The scale of the study comprises 22 plate elements in total. The varied parameters are the shear spans, profiled sheet types and sheet thicknesses. Each examined sheet has an undercut profile with additional embossment. On the basis of experimental results, the influences of the varied parameters and profile forms on the load-bearing and composite behaviour are discussed. This study provides important key findings which show that dense lightweight woodchip concrete can transfer sufficient longitudinal shear forces to the composite joint

Gravel wash mud, a quarry waste material as supplementary cementitious material (SCM)

The suitability of gravel wash mud (GWM), a sludge waste from gravel quarrying, is examined for its use as a partial Ordinary Portland cement (OPC) clinker substitute. The gravel wash mud was dried, milled into a fine powder and calcined at 750°C, 850°C and 950°C. In this study, various characterisation methods including particle size distribution (PSD), X-ray fluorescence (XRF), X-ray diffraction (XRD) and the simultaneous thermal analysis (STA) were applied on the calcined GWM powders to determine the optimal calcination temperature. Over 200 specimens were prepared based on different cement paste and mortar mixes to investigate the potential of calcined GWM powders as SCMs. The pozzolanic activity of the GWM powders was verified by applying strength-based evaluation methods, simultaneous thermal analysis and SEM on hardened samples. Very promising strength-enhancing capacities were observed for samples containing GWM powders calcined at 850°C with a OPC replacement level of 20 wt.%

Assessment of the suitability of gravel wash mud as raw material for the synthesis of an alkali-activated binder

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of an alkali-activated binder. The GWM powders were thermally treated at five different calcination temperatures 550, 650, 750, 850 and 950°C. The characterisation of the raw material comprises the particle size distribution (PSD) by laser granulometry, the chemical and mineralogical composition by X-ray fluorescence and X-ray diffraction analysis respectively, and simultaneous thermal analysis. The performance of the alkali-activated binders was examined using compression strength tests and the microstructure was observed using scanning electron microscopy (SEM). The GWM was classified as an aluminosilicate raw material with kaolinite and illite as main clay minerals. Furthermore, a mean particle size around 6.50μm was determined for the uncalcined and calcined GWM powders. The SEM images of the developed binders showed the formation of a compact microstructure, however, relatively low strengths were achieved. This preliminary study highlights an example of an aluminosilicate prime material, which shows very promising chemical and mineralogical characteristics, but its suitability for alkaline activation without further additives was not confirmed as far as performance-based criteria are considered

Mechanical characterisation of alkali activated clay - based geopolymer binder made out of gravel wash mud

One of the most promising cement alternatives are geopolymer cements. The term “geopolymer” was mentioned for the first time by Davidovits1 and classifies all forms of inorganic polymeric material synthesised by chemical reaction of aluminosilicates and an alkaline activating solution. The production of geopolymer binder comprises in two main procedures: calcination and geopolymerisation. The synthesised geopolymer shows interesting characteristics like good mechanical properties, high strength and good durability

Recycling of gravel wash mud for manufacturing CO2-reduced cement

The present research project “CO2REDCEM” is carried out at the Laboratory of Solid Structures (LSS) of the University of Luxembourg, in close collaboration with Luxembourgish industrial partners (Cimalux S.A., Carrières Feidt S.A. and Contern S.A.). This project aims at reducing the generation of CO2 emissions during cement production by minimisation of the use of cement clinker or its complete replacement by new binder compositions and concepts, containing novel material resources derived from local unused industrial waste products. Such a potential raw material is gravel wash mud (GWM), which occurs as a waste product from gravel mining. This clayey mud is collected from a sludge reservoir, located in the North West of Luxembourg. Currently, this waste product is landfilled without any further use. However, this prime material offers very promising properties, which require a thorough characterisation and verification before its revalorisation as a viable supplementary cementitious material (SCMs). Reusing or recycling of waste elements into goods has been among the greatest ambitions of our and earlier generations, and it will take a more important role in the future economy. One primary goal of this project is to replace the “end-of-life” concept of gravel wash mud by reusing it as new raw material. This endeavour will bring double benefit to environment as the waste is prevented from landfilling, and it is revalorised as a prime resource in another system.This research work shares the outcomes from the assessment of the performance of the prime material GWM within the following binder concepts and binder reaction mechanisms: • The use of gravel wash mud (GWM) powders as a precursor material for the synthesis of alkali-activated binders: A “cementless” binder is synthesised by alkaline activation of processed and calcined GWM powders. The mitigation of the CO2 emissions is achieved by the calcination process of the clayey gravel wash mud, which requires less thermal energy and thus lower energy consumption than for cement clinker production. • Substitution of Ordinary Portland Cement (OPC) by calcined GWM powders: Cement and concrete mixtures are prepared based on partial replacement of Portland cement by calcined GWM powders. This study presents the investigations on the involved reaction mechanisms (pozzolanic and cementitious hydration reactions), the optimal mixture configurations and the optimal material treatment processes. • The development of lime-Metakaolin-GWM binder concepts: Mixtures without cement are developed using GWM and other constituents, classified as industrial by-products. This research includes the mineralogical and microstructural characterisation of the constituents, the understanding of the reaction mechanism, and the optimisation of the mixtures to enhance the performance of the novel cementitious products. This thesis allowed to assess the performance of the waste product GWM as a valid pozzolanic prime material and to understand the requirements on physical, chemical and mineralogical characteristics of any potential raw material to ensure its permissibility as an alternative supplementary cementitious material (SCM)

Use of recycled concrete in construction in Luxembourg

Construction and demolition waste constitutes a major portion of total waste production in the world, and most of it is used in landfills. The re-use of concrete rubble collected from demolished structures is an important issue. After crushing and screening, there is the possibility of appropriately treating and reusing such waste as aggregate in new concrete, especially in lower level applications. Different aspects of the topic beginning with a brief review of the European initiatives and definition in terms of C&D waste generated and recycled aggregates produced from C&D waste are given. Along with a brief overview of C&D waste, a summary of the situation in Luxembourg in use of recycled aggregate is discussed. This writing concludes by identifying some of the major barriers in more use of recycled aggregate concrete, including lack of awareness, lack of knowledge, barriers of specifications/codes for reusing these aggregates in new concrete

Performance of lime-metakaolin pastes using gravel wash mud (GWM)

The performance of ternary binders using lime, metakaolin (MK) and gravel wash mud (GWM) powders is studied for the development of novel lime-pozzolan pastes. This study examines the influence of varying mixture proportions using different types and compositions of lime powders and GWM at different treatment levels on the mechanical properties of lime-MK-GWM pastes. Various characterisation techniques including particle size distribution (PSD), X-ray fluorescence (XRF), X-ray diffraction (XRD), compressive strength tests, simultaneous thermal analysis (STA) and scanning electron microscopy (SEM), were applied on the different raw materials, respectively, on the hardened pastes to determine the reaction kinetics, the resulting microstructure and the mechanical performances of the lime-MK-GWM binder systems. Higher strength-enhancing contributions of thermally treated GWM powders (calcined at 850°C) leading to compressive strengths up to 18 MPa were confirmed and the strength-based evaluations revealed that hydrated lime-based pastes achieved higher mechanical performances than hydraulic lime-based binder systems