Portland clinker from by-products and recycled materials out of the building and construction sector

Many companies are revising their business operations whilst gearing their pursuit of profitable growth to the assurance of environmental protection and quality of life for present and future generations. Even when this adaption is not desired, they are forced to it by economic necessity, public opinion or by governmental pressure to decrease their ecological impact. Based on this new perspective, some companies are thus beginning to make significant changes in their policies, commitments and business strategies. The cement manufacturing process consumes large quantities of non-renewable raw materials. This process is also an important source of CO2 emissions. Many initiatives are already taken to make the cement production processes more sustainable. The cement sustainability initiative is one example that demonstrates the global effort of the cement industry in pursuing sustainable development. This PhD study is elaborated in line with the cement sustainability initiative. It explores how the cement industry could integrate by-products or recovered materials out of the building and construction sector in their Portland clinker process, which is a part of the cement manufacturing process. Indeed, different producers and consumers within this sector could exchange materials or energy to pursue mutual ecological advantage. To determine the fitness of these by-products or recycled materials as alternative raw material, specific material properties important for Portland clinker production were investigated in a practical and objective way to not lose track with the real manufacturing process itself. To determine this specific fitness, a good evaluation of the physical, chemical and mineralogical composition and variation of these materials is necessary. Furthermore, theoretical simulations of alternative clinker compositions or artificial made Portland clinkers on lab scale have to be used to evaluate the impact of these materials on the Portland clinker process. It is quite difficult to realistically simulate clinker production on lab scale because of the specific construction of a clinker kiln. The typical properties of a kiln have to be taken into account while imitating the production process to generate an artificial clinker. Therefore, a specific set-up was used to make an objective evaluation of the fitness of an alternative raw material possible. Variations specific for the simulation itself were identified, avoided if possible and included in the evaluation of the final results if necessary. Three factories located in the Benelux were chosen to act as a reference for the Portland clinker process. By their different technical specifications as well as used Classic Raw Materials (CRM), they will deal in another way with these by-products or recycled materials resulting in specific mathematical simulations and the artificial produced clinkers which will differ from each other. Five specific material sources were investigated as possible alternative raw materials for Portland clinker production. Their recycling in the Portland clinker process could lower use of natural resources and counter landfill. They were specifically chosen to represent a wide variety of materials having their origin as by-product out of an existing production process or as waste material from demolished building or concrete constructions. First, the impact of by-products out of porphyry and dolomitic limestone aggregates production on Portland clinker production was investigated. Porphyry and dolomitic limestone aggregates represent a group of raw materials which are used at a daily base in many construction applications. The by-products are generated in the processing steps to improve the quality of the produced aggregates. In most cases, this improved aggregate quality will create an ecological benefit in the related applications such as concrete and asphalt. By avoiding waste disposal by landfill and a redistribution of the energy required for the aggregates production process, the valorisation of these by-products is also ecologically and economically beneficial for the aggregates manufacturing business itself. A recycling of both aggregate types at the end of a life cycle of a derived concrete or building material could also be a valid source for these types of materials. Neither porphyry nor dolomitic limestone is up until now used at regular base in Portland clinker production. This is partly due to the presence of high levels of MgO. MgO is avoided in Portland clinker production due to the specific limitations within national and international cement standards related to the risk of unsoundness of concrete. This investigation, nevertheless demonstrated that MgO, when cautiously introduced in line with well-defined limitations, should rather be taken into account for its positive mineralogical influence on clinker than avoided because of its possible periclase formation and related unsoundness properties. Valorisation of by-products of porphyry and dolomitic limestone materials in Portland clinker production could therefore be maintained as valuable and realistic solution. Secondly, materials out of niche markets for cement consumption in the form of non-asbestos fibrecement and cellular concrete were investigated. These materials show a limited chemical variation initiated by their specific production processes. Fibrecement as well as cellular concrete materials could have their origin as by-product out of their own production process or as demolition waste at the end of a life cycle. A small chemical variation of the raw material mix is a very important process parameter for Portland clinker production which substantiates the choice of these materials. Non-asbestos fibrecement is partly composed out of organic fibres as cellulose, polyvinyl alcohol and/or polypropylene which replaced asbestos in earlier versions of fibrecement. Furthermore fibrecement as well as cellular concrete contain organic contaminations in the form of glues, plastics, paint etc. when recycled out of an end of life cycle of a construction. Presence of organic components in the raw material mix could provoke blockage of the cyclone tower as well as generate a crossing of the TOC (Total Organic Carbon) emission limits at the chimney of the Portland clinker process. Nevertheless this investigation demonstrates that the presence of these organic constituents in a raw material, although better avoided, is not insurmountable if introduced at a specific point of the Portland production process. Non-asbestos fibrecement could for this reason be catalogued as a valid raw material for Portland clinker production. On the other hand, research on cellular concrete demonstrated that the presence of high levels of coarse quartz particles makes it a raw material unsuited for Portland clinker production. Fineness and particle size distributions affect the burnability of the raw material mix. A sufficient specific surface area has to be created to facilitate the sintering process and to decrease sintering temperature. Quartz (SiO2) particles although having a quite high mineral hardness have to be ground the finest to obtain optimal burnability of the raw material mix. Finally by-products out of common concrete production in the form of concrete sludge and waste materials out of demolished concrete in the form of fines fractions were investigated as raw material for Portland clinker production. Common concrete represents the biggest market as a function of cement consumption and is therefore a logical choice when investigating possible alternative raw materials out of the construction sector. For the evaluation of concrete sludge, eighty-seven samples were collected to have a good overview of its chemical variation. Out of this evaluation, it was concluded that the big chemical variation makes concrete sludge unsuited for Portland clinker production. Also the possible presence of coarse quartz particles was investigated and demonstrated to be a serious bottleneck although preparation phases by screening allowed to successfully decrease the presence of coarse quartz particles and to improve the related burnability of the alternative raw material mix. Nevertheless, these preparation phases turned out to be ineffective to improve the chemical variation. Concrete sludge has therefore to be avoided for Portland clinker production. Although fines fractions out of recycled concrete and concrete sludge originate both from the same base material, the fines fractions out of recycled concrete demonstrated to be different in terms of physical, chemical as well as mineralogical composition when compared to concrete sludge. A reduction in chemical variation of these fines fractions was obtained by the use of innovative separation techniques. Fines fractions seem to be a valid raw material if generated by these specific separation techniques. Nevertheless, more samples will be necessary to evaluate the chemical composition, the related dosing potential as well as the necessity of a homogenisation phase. The examination of the suitability of these five alternative raw materials for Portland clinker production is also an effort to determine attention points and thus facilitate future evaluations of other materials than those investigated in this PhD study. These attention points are related to specific properties of a material such as its chemical variation, the presence of organic constituents, its average chemical composition, fluxing effects due to the presence of some minor components, its particle size distribution as a function of its mineralogical composition, and possible material preparations phases. The fitness of a material as alternative raw material for Portland clinker production will be a combination of each of these points and their combined impact on the Portland clinker process and the final Portland clinker quality. At the one hand, using an alternative raw material could improve the environmental impact of its proper production process and decrease waste disposal by landfill. Nevertheless, on the other hand, it could be classified as a non-sustainable solution if it has a negative influence on the Portland clinker process and final clinker quality. Indeed, the environmental impact analysis of the specific valorisation of an alternative raw material in Portland clinker production has to be an objective evaluation of pro’s and con’s, to determine whether it can be classified as a next step in the continuing sustainable development of the cement production process, or better be avoided due to the additional insurmountable energy expenditure for alternative raw material valorisation or/and an adverse impact on the Portland clinker process and quality. Although no sufficient data were available to perform an objective LCA (Life Cycle Assessment) on the use of each of the five investigated materials in the Portland clinker production or the production processes where they originated from, an evaluation based on the normalised guidelines of the LCA procedure was still possible

Improving the quality of various types of recycled aggregates by biodesposition

Demand for construction materials has been rising in recent decades in many countries around the world, placing a heavy burden on the environment in terms of both the natural resources consumed and the enormous flow of waste generated. In order to obtain a more sustainable construction, it is often suggested to reintroduce the industry’s own waste as input for the manufacture of new materials. In this study, the use of construction and demolition waste of concrete or mixed concrete/ceramic nature is investigated as a replacement of natural aggregates in concrete. The greater affinity of recycled aggregates for water directly affects the workability and/or the concrete strength and durability. One possible solution to reduce the aggregates water absorption is to apply a biogenic treatment with calcium carbonate-precipitating bacteria that consolidate the aggregate surface or the adhering mortar. Experimental results show that the biodeposition treatment reduced the recycled aggregate water absorption by generating precipitation in the pores and an impermeable outer layer, most effectively on the roughest particle surfaces. The largest decrease happened in the aggregates with the highest porosity. The biogenic layer had a good cohesion with the aggregates. The results of sonication indicated that the most effective treatment was on recycled concrete aggregates (RCA) instead of mixed aggregates (MA). Therefore, the treated RCA was used to make concrete for further investigation. The concrete made with bio-treated RCA had a denser structure, a decreased water absorption (around 1%) and an improved compressive strength (25%)

Microbial carbonate precipitation for the improvement of quality of recycled aggregates

High water absorption is the main drawback of recycled aggregates which greatly hinders the re-use of them in concrete production. In this study, bio-deposition treatment, based on bacterially induced CaCO3 precipitation, was applied to improve the quality of the recycled aggregates. Two representative recycled aggregates, recycled concrete aggregates (CA) and mixed aggregates (MA) were used. The bacterial CaCO3 precipitated on the surface and in the pores of the recycled aggregate worked as a barrier for the penetration of water, and hence the water absorption of the aggregates can be decreased. Firstly, the optimal treatment method was determined by screening among spraying and several immersion strategies. It was found that the two times immersion treatment was the best method. Samples subjected to this method had a high weight increase (2% for CA and 2.5% for MA) and largest extent of water absorption decrease (one percentage point drop for CA and two percentage points drop for MA). Furthermore, The biogenic CaCO3 had a good cohesion and strong bond with the aggregate surface. Very limited (< 0.1%) mass loss occurred on the bio-treated samples while the mass loss of the untreated aggregates was much higher (0.2% for CA and 0.5% for MA). This indicated that the surface of the aggregates was strengthened by the biogenic CaCO3 as well. After using the bio-treated aggregates, the compressive strength was increased by 40% for CA concrete and 16% for MA; the water absorption was decreased by 27% for CA concrete and 20% for MA concrete. (C) 2017 Elsevier Ltd. All rights reserved

MgO as fluxing agent for a sustainable Portland clinker production

MgO in clinker and cement is generally related to the soundness of concrete by the presence of periclase. MgO is also described in literature as a possible fluxing agent in combination with R2O (R = Li, Na, K) and SO3 which could increase alite (C3S) formation and lower the temperature of the liquid formation in Portland clinker production. This fluxing effect could improve the burability of the Cold Clinker Meal (CCM) and could lower the energy consumption of a clinker kiln. By using fines and sludge generated out of the production of porphyry and dolomitic limestone aggregates as Alternative Raw Material (ARM), an effort was made to create this effect in a practical way. Simulations were carried out, CCMs were composed and experimental clinkers were sintered with dosages of fines and sludge that were maximised but esteemed as realistic. The final clinkers were fully analysed and evaluated on possible mineralogical influences

Feasibility study on the use of cellular concrete as alternative raw material for Portland clinker production

This paper aims to investigate the use of cellular 'concrete as an alternative raw material (ARM) for Portland clinker kilns. The possibility to generate a raw material with a stable compositional variation was investigated as well as simulations were carried out to maximise their use in clinker kilns. Based on these simulations, experimental clinkers were produced with dosages that were esteemed as realistic. Because of the presence of important levels of quartz sand in the cellular concrete materials, the energy necessary to grind the alternative raw material in comparison with comparable classic raw materials was investigated as well as the influence of the final particle size distribution of the Cold Clinker Meal (CCM) on the mineralogical composition of the final clinkers. It will be demonstrated that cellular concrete materials can be used as ARM for clinker production although there are some important restrictions that will limit the practical implementation. This investigation will also provide some interesting knowledge on the use of other recycled concrete materials as alternative raw material for Portland clinker production

Fibrecement recycling as raw material for Portland clinker production

This paper aims to examine the use of fibre cement waste as an alternative raw material for clinker kilns with enumeration of the possible limitations. The ultimate aim is to find a nobler use for fibrecement waste and to develop a more sustainable production of Portland clinker by saving natural resources and with a potential effect of reduction of CO2 emissions. Numerical simulations are carried out to maximize the use of fibrecement waste in clinker kilns, taking into account the chemical variation of the waste, its behaviour within a clinker kiln, the impact on energy consumption and finally the influence on the carbon footprint calculated from the decarbonation and the fuels used. Furthermore, experimental clinkers are produced and analysed according to the above described concept and corresponding with waste dosages that are esteemed as realistic. The use of fibre cement waste as an alternative raw material was found to be possible, without compromising the physical, chemical or mineralogical properties of the clinker