Cement-based Construction Materials Research Articles

Automated detection and segmentation of concrete air voids using zero-angle light source and deep learning

The detection and segmentation of air voids in concrete has received significant attention because they are critically important for determining concrete properties and performance. However, previous methods have shown low efficiency and accuracy in void segmentation. Particularly, it remains difficult to detect and segment irregularly shaped voids, especially those that are connected and have indistinct boundary features. This study presents a zero-angle light source to clearly capture features of different types of voids that are otherwise hard to identify using conventional illumination schemes, thus allowing for accurate segmentation of complex air voids by an instance segmentation model using a path aggregation network (PANet). The PANet model significantly outperforms existing semantic segmentation algorithms in detecting air voids, especially small and connected ones. Furthermore, we also show the robustness and generalization ability of this model for air void segmentation and analysis by applying it to different cement-based construction materials.

Recent Advances in Fly-Ash-Based Geopolymers: Potential on the Utilization for Sustainable Environmental Remediation.

This Mini-Review provides the fundamentals and the state-of-the-art overview on geopolymers, novel inorganic polymeric materials (also known as alkali-bounded ceramics), synthesized from aluminosilicate sources and explores their current and potential sustainable environmental applications. It summarizes and examines concisely the recent scientific advances on geopolymers widely synthesized from abundantly available fly-ash-based aluminosilicate materials via alkaline activation at relatively low temperatures. Although geopolymerization is not a new concept and has offered valuable solutions to some environmental challenges as a low-cost and environmentally benign alternative to conventional energy-intensive Portland cement-based construction materials and has also been used as a barrier in immobilizing toxic and radioactive metals, the application of this technology to produce effective adsorptive materials for mitigation of liquid- and gas-phase contaminants is relatively recent. The valorization of the fly-ash waste in the sustainable and cost-effective development of geopolymeric adsorbents and catalysts for the treatment and control of environmental contaminants and energy production and storage could lead to many economic benefits due to the low cost and resource recycling of this globally abundant raw material. Perspectives on the synthesis and utilization of new geopolymer-based adsorbents for environmental and energy applications with insights into future research directions, prospects, and challenges for economic large-scale production are addressed.

Recycling hazardous water treatment sludge in cement-based construction materials: Mechanical properties, drying shrinkage, and nano-scale characteristics

Water treatment sludge (WTS) management is a growing global problem, which is often disposed as a hazardous material in landfill space. This paper aims to use modified WTS as a novel supplementary cementitious material, by determining the effects of calcined WTS addition on the composition and performance of Portland cement composites. The effect of WTS to replace cement partially by weight on the mechanical properties and drying shrinkage of specimens has experimentally been studied, and the internal microstructure is also determined by scanning electron microscope and nanoindentation techniques. The results showed that mortar with 10% modified WTS presented higher 90-day compressive strength although specimens with 20% and 30% modified WTS showed 10.54% and 16.20% reduction compared to the control group. Meanwhile, the modified WTS has pozzolanic activity and can react with cement hydration products to increase the compactness of the microstructure, thereby reducing the drying shrinkage of the pastes (10% modified WTS). When 10% of the cement was replaced by modified WTS, the volume fraction of unhydrated clinker and pore phase in the matrix decreased significantly, while the volume fraction of C–S–H phase increased. In addition, the interface transition zone (ITZ) width of the specimen (10% WTS) is the smallest, and as the replacement rate of modified WTS increases, the ITZ width of the specimen increases significantly. This paper proves that the modified WTS, as a supplementary cementitious material, can be considered a feasible and sustainable alternative for use in the building materials.

Toxicity of cement-based materials

Clinker production represents a high percentage of global CO2 emissions and a significant decrease by 2030 is mandatory. Therefore, there is a permanent search for innovative and sustainable cement-based construction materials (CBM) around the world. The increased development and demand of sustainable construction solutions pushed the incorporation of nontraditional raw materials in CBM mixes. Due to the insufficient knowledge on the use of these components, it is fundamental to perform studies to assess their toxicological effects on the relevant environmental compartments. Some studies are found in the literature that analysed the environmental impacts of new CBM but there are not many that include a toxicity analysis. The procedures followed in the latter are varied since there were no specific recommendations to analyse construction materials until 2017, and the results were obtained following different standards or directives. Therefore, the direct comparison of the results of these studies is generally not possible. In that year, a guidance on the use of ecotoxicity tests on construction products was published - technical report CEN/TR 17105:2017 (Construction products - Assessment of release of dangerous substances). Nevertheless, the process to evaluate the potential toxicity of construction materials is complex, but fundamental. In fact, there is no direct correlation between existing metals’ concentration in one product and leached metals’ concentration, which makes it difficult to know the toxicity level. The aim of this paper is to review and present available CBM toxicity information, including standards, databases or labels. The tools that already exist to support the evaluation of the toxicity risks of CBM will also be analysed. Based on this, an approach for the toxicity evaluation of CBM is proposed in order to provide researchers with real-time support for the development of sustainable CBM with reduced risks associated with toxicity.

Mechanical and Thermal Performance of Cement Mortar Incorporating Super Absorbent Polymer (SAP)

Super Absorbent Polymer (SAP) is a favorable admixture which can influence various properties of cementitious materials. It mainly improves the water retaining properties of cement-based construction materials. In this paper, an experimental program was carried out to determine the mechanical and thermal performance of cement plaster containing SAP. Firstly, the absorption capacity of SAP was determined in different loading conditions and chloride solutions. Thereafter, the optimum dosage of SAP for cement plaster was also determined from five different proportions of SAP (0.05, 0.1, 0.3, 0.5 and 1% of cement mass) based on the compressive strength test results. The mortar incorporating 0.05% SAP of cement mass was selected as the optimum dosage, which yielded the highest compressive strength. Two slabs of 1×1×25 mm with 0.05% SAP and two slabs of 1×1×25 mm without SAP were cast to determine the thermal performance of the cement mortar with and without SAP. For this purpose, a wooden chamber of 2×1×1 m was constructed and the slab was placed in the middle of this chamber to carry out the thermal performance test of cement mortar. The slabs with 0.05% SAP showed promising results for acting as a thermal barrier in buildings compared to slabs without SAP. Doi: 10.28991/cej-2020-03091614 Full Text: PDF

Resistance of fly ash geopolymer binders to organic acids

Fly ash geopolymers are a relatively new class of binders with the potential to reduce the CO2 emissions associated with Portland cement based construction materials. This paper reports on the organic acid resistance of fly ash geopolymers following exposure to acetic and lactic acid. Organic acids are prevalent in many circumstances including agriculture, production processes and waste management. These findings demonstrate that the surface of fly ash geopolymers had superior resistance to organic acids when compared with traditional Portland cement, evidenced by smaller mass losses. This was attributed to the formation of reaction products which were less susceptible to acid attack than those formed in Portland cement systems due to their lower calcium content. However, despite the surface of fly ash geopolymers appearing less deteriorated due to organic acid attack, they were found to have a higher porosity than their Portland cement counterparts making them more susceptible to acid ingress.

Heterogeneous Nature of Calcium Silicate Hydrate (C-S-H) Gel: A Molecular Dynamics Study

Structure and mechanical properties of Calcium silicate hydrate (C-S-H) at a molecular level act as “DNA” of cement-based construction materials. In order to understand loading resistance capability of C-S-H gel, research on molecular dynamics (MD) was carried out to simulate the uniaxial tension test on C-S-H model along x, y, and z directions. Due to the structure and dynamic differences of the layered structure, the C-S-H model demonstrates heterogeneous mechanical behavior. On an XY plane, the cohesive force can reach 4 GPa which is mainly provided by the Ca-O and Si-O ionic-covalent bonds. The good plasticity of calcium silicate sheet is attributed to the silicate branch structure formation and the recovery role of interlayer calcium atoms. However, in z direction, C-S-H layers connected by the unstable H-bonds network, have the weakest tensile strength 2.2 GPa. This results in the brittle failure mode in z direction. The relatively low tensile strength and poor plasticity in z direction provides molecular insights into the tensile weakness of cement materials at macro-level.

Effects of microwave, thermomechanical and chemical treatments of sewage sludge ash on its early-age behavior as supplementary cementitious material

To better inform the recycling of sewage sludge ash (SSA) in cement-based construction materials, this laboratory study investigated a variety of modification methods aimed at improving the value of SSA. For pre-treatment, three different methods of physical modification including low-temperature drying, grinding, high-temperature calcination were selectively performed. Microwave treatment was also explored as an alternative to the calcination procedure. Subsequently, chemical modification of the SSA was performed by blending with quicklime (QL) for likely chemical activation. The effectiveness of these treatments was assessed in terms of leachability of heavy metals out of the treated SSA and the reduction in total organic carbon (TOC). High-temperature calcination of SSA enhanced the immobilization of heavy metals (e.g., Mn, Zn, and Ba). In contrast, the QL treatment helped immobilize some heavy metals (e.g., Mn and Zn) but re-liberated other metals (e.g., Ba). Compared with calcination at 500 °C for 2h, 15-min microwave heating of pre-treated SSA exhibited better performance in immobilizing the heavy metals and nearly as good performance in reducing the TOC in the SSA Finally, based on the compressive strength data of the cement pastes, microwave treatment is an effective alternative to thermal calcination, in terms of mitigating the side effects of admixed SSA on the cement hydration.

Evaluation of the Ecotoxicological Potential of Fly Ash and Recycled Concrete Aggregates Use in Concrete

This study applies a methodology to evaluate the ecotoxicological potential of raw materials and cement-based construction materials. In this study, natural aggregates and Portland cement were replaced with non-conventional recycled concrete aggregates (RA) and fly ash (FA), respectively, in the production of two concrete products alternative to conventional concrete (used as reference). The experimental program involved assessing both the chemical properties (non-metallic and metallic parameters) and ecotoxicity data (battery of tests with the luminescent bacterium Vibrio fischeri, the freshwater crustacean Daphnia magna, and the yeast Saccharomyces cerevisiae) of eluates obtained from leaching tests of RA, FA, and the three concrete mixes. Even though the results indicated that RA and FA have the ability to release some chemicals into the water and induce its alkalinisation, the respective eluate samples presented no or low levels of potential ecotoxicity. However, eluates from concrete mixes produced with a replacement ratio of Portland cement with 60% of FA and 100% of natural aggregates and produced with 60% of FA and 100% of RA were classified as clearly ecotoxic mainly towards Daphnia magna mobility. Therefore, raw materials with weak evidences of ecotoxicity could lead to the production of concrete products with high ecotoxicological potential. Overall, the results obtained highlight the importance of integrating data from the chemical and ecotoxicological characterization of materials’ eluate samples aiming to assess the possible environmental risk of the construction materials, namely of incorporating non-conventional raw materials in concrete, and contributing to achieve construction sustainability.

The use of Biochar to reduce the carbon footprint of cement-based materials

The organic waste management is a most current topic, because its processing and degradation it is responsible for emissions of methane and other greenhouse gases, leading to serious environmental problems. Limited oxygen thermochemical processes, such as pyrolysis or gasification, have demonstrated the energy recovery potential of the treated biomass and its environmental benefits. However, the solid part of the process -Biochar- it is considered as a waste, as only its coarse ash can be used as soil improvers. Nevertheless, several researchers have explored its potential application as green filler in order to reduce the carbon footprint both of cement production and cement-based construction materials. In this work, Biochar microparticles were used both as a filler inside the cement paste and mortar composites and as a substitute for the cement powder inside the mixes. Based on previous work, this investigation has a twofold objective: to understand the full influence of the use of an optimized percentage of Biochar (2% with respect to the weight of the cement) either as a filler in the mixture or as a substitute for cement, while guaranteeing an improvement in the strength without losing ductility. The results showed that 2 wt% of Biochar’s particles are sufficient to increase the strength and toughness of the cement and mortar composites and, in place of the cement in the mixture, can maintain the mechanical properties equal to those of the reference samples.

Recycling hazardous textile effluent sludge in cement-based construction materials: Physicochemical interactions between sludge and cement

The textile industry produces a large amount of textile effluent sludge (TES). Many studies have explored the potential use of TES in cement-based materials. However, the physicochemical interactions between the TES and ordinary Portland cement (OPC) have rarely been studied. In this study, the effects of increasing dosage (0–20% by OPC) of TES on the performance of OPC-TES blends were investigated in terms of hydration progress, mechanical strength, microstructure evolution and metal leachability. The results showed that TES markedly delayed the OPC hydration at the early age, and increasing dosages of TES decreased the portlandite content at 7 and 28 days’ age. Compared to the reference, the OPC-TES mortar exhibited seriously degraded mechanical strength; when using 20% TES, the decrease in compressive and flexural strength reached up to 71% and 42% respectively at the age of 28 days. Scanning electron microcopy and mercury intrusion porosimetry found the inclusion of TES introduced more weak interfaces in the cement mortar, thus increased the total porosity especially the macropores. But leachability tests revealed all the toxic metals in the TES were stabilized after the incorporation of OPC and exhibited very low metal mobility in the OPC-TES mortar, which posed no environmental risk.

AC electrical properties of geopolymers with carbon black admixture

Geopolymers as competitors to the cement-based construction materials are intensively studied in the present. Their competitiveness mainly arises from their high strength, favourable development of hydration heat at early age, good chemical resistance and thermal stability. Further qualitative improvement of functional properties can be achieved by adding electrically conductive admixtures. In an appropriate amount (called percolation threshold), mechanical properties remain reasonable and electrical properties become sufficient to ensure evolution of heat by acting of an external power source (self-heating), to detect material damage (self-sensing) or to harvest thermoelectric energy (energy harvesting). In this paper three geopolymers with different dosages of carbon black (CB) admixture (0 wt. %, 4 wt. %, 10 wt. %) were studied by means of LCR bridge AC measurements. It was observed significant difference in electrical behavior of the studied geopolymers. 0 wt. % geopolymer exhibited highly capacitive character, 4 wt. % geopolymer was slightly shifted to resistive behavior and 10 wt. % geopolymer behaved like resistor even to high frequencies with reasonable resistance which indicates its possible self-heating ability.

Wood-based support material for extrusion-based digital construction

Purpose Extrusion-based digital construction (DC) approaches make it feasible to overcome constraints of conventional construction, namely, high formwork costs, long total construction times, low productivity and geometrical inflexibility. However, to date, no satisfactory solutions for extruding strongly inclined and horizontal elements are available. A wood-starch-composite has been systematically developed as a sustainable support material (SM) for extrusion-based DC. Design/methodology/approach Material and process-specific requirements were identified for this purpose, and a feasible process chain was developed. A parametric study was conducted to determine the influence of SM composition on its extrusion feasibility and compressive strength. Various compositions with two starch types and two wood particle shapes were tested. New, specific testing methods were developed. Selected compositions were tested using a 3D-printing device to verify extrudability and form stability. Findings Relationships between material compositions of SM and its rheological and mechanical properties were identified. All mixtures showed sufficient compressive strength in respect of the loading conditions analysed. However, their flow properties varied significantly. A mixture of native maize starch and wood floor was identified as the best variant (compressive strength 2.3 MPa). Research limitations/implications Comprehensive investigations of possible process chains, as well as full-scale demonstration and optimisation of the process parameters, were not in the scope of this paper. Such investigations are intended in further studies. Practical implications The general applicability of wood-based SM for DC with cement-based construction materials was proved. Originality/value The findings offer a novel and promising solution for 3D-printing of non-vertical concrete elements. Experimental setup and material compositions are detailed to ensure reproducibility.

Hydration of Reactive MgO as Partial Cement Replacement and Its Influence on the Macroperformance of Cementitious Mortars

A recent quest for more sustainable cement-based construction materials has triggered the pursuit of technically viable alternatives of cement, making reactive magnesium oxide (MgO) one of the least known top contenders to reduce this sector’s environmental impact since it participates in the cement’s hydration reactions and presents enhanced carbon capture ability during its life cycle. In this study, two different commercially available reactive MgO samples were evaluated as partial cement replacements (at 10%, 15%, and 20%, by weight) in the production of mortars. Thermogravimetric analysis (TGA), energy-dispersive X-ray (EDX) analysis, differential thermal analysis (DTA), and powder X-ray diffraction (XRD) analysis of cement, MgO samples, and resulting mortars were carried out. All specimens were evaluated in terms of their mechanical and durability-related performance (i.e., flexural and compressive strength, carbonation, water absorption by capillary action, and shrinkage). The main results suggest that, in spite of the decreased, albeit acceptable, performance with increasing incorporation of MgO as partial cement replacement, a significant decrease was observed in the shrinkage strain of cementitious materials.

Compressive Strength and Leaching Behavior of Mortars with Biomass Ash

This study investigated the use of a biomass ash produced by a fuel combination made with wood, corn stover, and corn cob as cement replacement for the production of mortar. Biomasses are now widely accepted as a substitute for conventional fuels and are becoming essential for cost-effective production of energy. This study aimed to provide an opportunity for the annual agricultural corn-crop residue, corn stover and cob, which is increasingly being used as fuel for its valuable energy content. Measurements of workability, compressive strength, and leachate properties (pH, salinity, heavy metals and calcium ion release) of mortar specimen, at different cement substitution levels and ages, were evaluated. The results obtained reveal definitive possibilities for such mixed biomass ash to be used in cement-based materials, such as mortars. Moreover, a multiple regression analysis has been reported between the mass of calcium ions leached and the mixture composition with the compressive strength. Data show that further confirmation, on a longer span of time and of other types of mechanical properties and environmental tests, would be necessary to fully implement the use of such biomass ashes in various types of cement-based construction materials, in order to divert them from landfill disposal.

Experimental evaluation of the effect of mix design ratios on compressive strength of cement mortars containing cement strength class 42.5 and 52.5 MPa

Cement mortar is one of the major cement-based construction materials and its mechanical properties perform an important role in the strength of structures. The effect of different mortar mix design parameters on its compressive strength has always been of great significance. Specifically, this research investigates the simultaneous effect of cement strength class and sand-cement (S/C) and water-cement ratios (W/C) on the compressive strength of mortars containing with cement strength class 42.5 and 52.5 MPa. For this purpose, an extensive experimental plan with 540 cubic 50 mm specimens made with 36 different mix designs. The results showed that the compressive strength of specimens increased with age and was strongly influenced by cement strength class, S/C and W/C ratio. The optimal mix design in terms of compressive strength is the with S/C ratio of 2.75, W/C ratio of 0.3, and cement strength class of 52.5 MPa.

Development of New Eco-Efficient Cement-Based Construction Materials and Recycled Fine Aggregates and EPS from CDW

Background:This research paper presents the results of the characterization and adaptation of the construction product developed by the Experimental Centre of Production of the Faculty of Architecture, Design and Urbanism of the University of Buenos Aires, Argentina (CEP FADU UBA) for Spanish regulations. Additionally, it shows the study of the industrialization of its manufacturing process in Spain. The product consists of a cement-based compound that includes recycled fine ceramic aggregates and EPS from rehabilitation works.Objectives:The aim of this research work is to propose a new eco-efficient construction product adapted to Spanish and European regulations in order to minimize the environmental impact of the construction activity, improve energy efficiency and reduce construction costs. Furthermore, it is presented as a solution to the problem that construction and demolition waste management represents.Method and Results:Samples have been tested to the water absorption and compression resistance tests according to UNE standards. These parameters serve to delimit its use in new sustainable constructive solutions for the design of zero energy consumption buildings (nZEB).Conclusion:Results show that it is possible to obtain certain samples that include recycled ceramic aggregates and EPS which present good response to the mechanical and water absorption tests. In addition, it is obtained that industrializing this product in Spain is complex due to the current waste management system.

A review of characterisation methods for superabsorbent polymer (SAP) samples to be used in cement-based construction materials: report of the RILEM TC 260-RSC

Superabsorbent polymers (SAPs) have proven to be a very promising admixture which can positively influence various properties of cement-based materials. SAP samples intended for such use should be pre-tested with respect to their absorptivity as well as their kinetics of ab- and desorption prior to implementation in concrete or mortar. This not only reduces workloads in concrete laboratories in pre-testing modified cement-based mixtures but in fact discloses essentials of the eventual performance of the SAP in concrete and other cementitious materials. The review at hand outlines fundamentals of the thermodynamics of polymer chemistry as a basis for the sorptivity tests. The importance of the ionic composition of the test liquids and the interplay among expansive (swelling) and collapse-causing chemical forces in the hydrogel network are highlighted. Methods of free sorptivity testing in adequate saline solutions as well as absorbency determined subject to the application of external forces are summarised. Advantages and drawbacks of these methods are discussed, including a validation of anticipatory evaluations of SAPs’ performance as admixtures in cement-based building materials. Apart from sorptivity pre-tests several methods of instrumental analytics for the chemical characterisation of SAP samples are drawn up, which represent standard approaches of polymer-chemical analytics.

Application of carbonate precipitating bacteria for improving properties and repairing cracks of shotcrete

Shotcreting is a construction technique commonly used in many civil and mining engineering applications. Cracking is an unavoidable and inherent weakness of most cement-based construction materials including shotcrete. In this study, the effect of Bacillus Subtilis on healing and mechanical properties of shotcrete was evaluated. For this purpose, bacteria were introduced into mix design and curing solution in order to examine the effect of each approach on the compressive strength, tensile strength, permeability, porosity and healing of shotcrete specimens. The results of uniaxial compressive test showed up to 30% increase in the compressive strength of bacteria-exposed shotcrete specimens compared to control specimens. This strength improvement was 10% more in shotcrete specimens than in the conventional cast concrete specimens with the same mix design. The presence of bacteria, both in the mix design and curing solution, was found to enhance the tensile strength and decrease the water absorption and porosity of shotcrete. The maximum reduction in water permeability at 28days was observed in the specimens cured in the bacteria-containing solution. The ability of bacteria to heal the cracks created in the specimens was also evaluated in the present work. Bacterial precipitation of calcium carbonate in the pores of specimens was confirmed by SEM/XRD analysis. The results give clear evidence supporting the utility of calcium carbonate precipitating bacteria for healing the cracks and improving the durability of shotcrete.

On the use of crystalline admixtures in cement based construction materials: from porosity reducers to promoters of self healing

The project detailed in this paper aims at a thorough characterization of the effects of crystalline admixtures, currently employed as porosity reducing admixtures, on the self-healing capacity of the cementitious composites, i.e. their capacity to completely or partially re-seal cracks and, in case, also exhibit recovery of mechanical properties. The problem has been investigated with reference to both a normal strength concrete (NSC) and a high performance fibre reinforced cementitious composite (HPFRCC). In the latter case, the influence of flow-induced fibre alignment has also been considered in the experimental investigation. With reference to either 3-point (for NSC) or 4-point (for HPFRCC) bending tests performed up to controlled crack opening and up to failure, respectively before and after exposure/conditioning recovery of stiffness and stress bearing capacity has been evaluated to assess the self-healing capacity. In a durability-based design framework, self-healing indices to quantify the recovery of mechanical properties will also be defined. In NSC, crystalline admixtures are able to promote up to 60% of crack sealing even under exposure to open air. In the case of HPFRCCs, which would already feature autogenous healing capacity because of their peculiar mix compositions, the synergy between the dispersed fibre reinforcement and the action of the crystalline admixture has resulted in a likely ‘chemical pre-stressing’ of the same reinforcement, from which the recovery of mechanical performance of the material has greatly benefited, up to levels even higher than the performance of the virgin un-cracked material.