Search

This study examines an attempt to produce self-compacting concrete (SCC) containing fly ash (FA), ground granulated blast furnace slag (S) and both (FA + S). The effects of these materials on the rheological properties of the SCC mixes were studied experimentally. The study began with three groups of SCCs, each with 25% water binder (w/b) and 550 kg/m3 total binder content. Instead of superplasticizers (SP), the chemical admixtures were lignosulphonates (LS), which replaced Portland cement (PC) at levels by weight of 10%, 20%, 30% 40%, 50%, and 60%. The fresh properties of the mixtures were examined experimentally for slump flow diameter, T50 time, V-funnel time, and L-box height ratio. In the mixtures with FA alone, a continuous decrease was observed in compressive strength. Increases in strength ended at 40% in the case of FA alone, and 30% for both the S and FA + S mixes. Statistical analysis was carried out to assess the effect of experimentally substituted materials FA and S, with results showing that S had a greater influence than FA on T50 time, V-funnel, L-box height ratio, and compressive strength, while FA had more effect than S on the slump flow diameter test.

Hydrated cement is one of the complex composite systems due to the presence of multi-scale phases with varying morphologies. Calcium silicate hydrate (C–S–H), which is the principal binder phase in the hydrated cement, is responsible for the stiffness, strength, and durability of Portland cement concrete. To understand the mechanical and durability behavior of concrete, it is important to investigate the interactions of hydrated cement phases with other materials at the nanoscale. In this regard, the molecular simulation of cement-based materials is an effective approach to study the properties and interactions of the cement system at the fundamental scale. Recently, many studies have been published regarding atomistic simulations to investigate the cement phases to define/explain the microscopic physical and chemical properties, thereby improving the macroscopic performance of hardened binders. The research in molecular simulation of cementitious systems involves researchers with multidisciplinary backgrounds, mainly in two areas: (1) cement chemistry, where the hydration reactions govern most of the chemical and physical properties at the atomic scale; and (2) computational materials science and engineering, where the bottom-up approach is required. The latter approach is still in its infancy, and as such, a study of the prevailing knowledge is useful, namely through an exhaustive literature review. This state-of-the-art report provides a comprehensive survey on studies that were conducted in this area and cites the important findings.

An attractive approach to reduce the carbon dioxide footprint of deep soil mixing (DSM) is to replace Portland cement-based binders by geopolymers based on metakaolin. Safe design requires a good understanding of the mechanical and hydraulic properties of the improved ground, but very little is known about metakaolin–soil mixtures. For instance, shrinkage during curing is a significant issue for metakaolin-based concretes but has not been previously studied in soilcretes. In this work the permeability and strength of sand- and silty sand-based metakaolin soilcretes are studied under different curing conditions. The development of microcracks induced by geopolymer shrinkage is confirmed through a microstructural study using mercury intrusion porosimetry, scanning electron microscopy and X-ray computed tomography. The influence of microporosity and binder filling on permeability and strength is clarified adapting well-established soil models. A modified Kozeny–Carman formulation is proposed for permeability. A mixture ratio model is calibrated to represent strength. In general, the metakaolin-stabilised materials present excellent mechanical and hydraulic properties, although these are very sensitive to curing conditions.

The purpose of this study was to determine the effect of partial replacement of cement with diatomaceous earth (DE) on the compressive strength and absorption of mortar. The cement volume was replaced by different contents of replacement levels of 0%, 10%, 20%, 30% and 40% DE. Ordinary Portland Cement (OPC) and Portland Composite Cement (PCC) were used while the binder and sand were mixed at 1: 2 and 1: 4 vol ratios. Moreover, 5 × 5 × 5 cm3 cubes were used as the test specimens and their compressive strength was determined at 1, 3, 7, and 28 days while the absorption was evaluated at the curing age of 28 days. The results showed that the compressive strength of mortar with OPC for both 1: 2 and 1: 4 ratios decreased with the increment in the content of the DE. However, at 40% cement replacement, the mortar with OPC was categorized as type M according to SNI 6882:2014 or ASTM C270-10 with 28 days compressive strength observed to be greater than 17.2 MPa. Meanwhile, the mortar with PCC for 1: 2 was observed to have the highest compressive strength of 36.63 MPa at 20% cement replacement and 25.39 MPa at 10% cement replacement for 1:4. Furthermore, the absorption of mortar with DE was observed to be greater than for mortar with cement only.

The production of cement is a carbon dioxide-intensive process. Replacing ordinary Portland cement (OPC) with industrial by-products can bring down the carbon footprint associated with cement production. Various industrial residues are currently used as alternative cementitious materials in this regard. However, developing a low carbon dioxide composite cement with different pozzolans alters the packing density, which influences its properties. Although studies have been conducted on the use of fly ash and slag at lower cement replacement levels, studies on the packing density and strength of ternary and quaternary composite cements with higher replacement levels are limited. In this study, fly ash, blast-furnace slag, ultra-fine fly ash and ultra-fine slag are used as a partial replacement for cement in various proportions. Out of the 51 mixtures tested in the study, 11 combinations were selected, based on the maximum packing density, for further investigations on fresh and hardened properties to arrive at the best trade-off between cement reduction and desired properties. The early-age strength is influenced by the packing density of composite cements, whereas the later-age strength is found to be highly governed by the amount of OPC and the pozzolanic potential of the industrial by-products.

Geopolymer is an eco-friendly material used as an alternative to Portland cement and it can be used in construction practices as a repair material to concrete/as a structural element in construction/ as a whole. This study was mainly intended to understand the efficiency of geopolymers in the structural system when special concretes are involved in construction. Shear bond strength was evaluated for the combination of self compacting geopolymer concrete (SCGC) and normal self compacting concrete (SCC). SCGC was developed under external exposure curing conditions enabling it to be used in cast-in-situ production. This was achieved by binary blending of mineral admixtures, use of activator solutions, and superplasticizer. Comparative study on two types of push-off tests namely (1) Conventional Push-off test (Type 1) and (2) Push-off test with normal load acting over the shear interface (Type 2) were conducted to evaluate the interface shear strength. Test results were compared with selected shear friction models available from literature and the effect of introducing self compacting geopolymer concrete in composite interfaces were analyzed.

Recent developments in the infrastructure urged the requirement of developing concrete with high performance. This research work presents the development of sustainable High Strength Fiber Reinforced Concrete (HSFRC), and its mechanical properties such as compressive strength, tensile strength and flexural strength compared to conventional High Strength Concrete (HSC). Ordinary Portland Cement (OPC) was replaced with optimum amount of Micro-Silica (MS) and Pumice Powder (PP) by 15% and 10%. Hybrid Fibers (HF) are added in the mix of 1.5% by volume of concrete. The fibers used are Steel Fiber (SF), Poly-Propylene Fiber (PPF), Basalt Fiber (BF) and Carbon Fiber (CF). Effect of fiber and its performance are compared with conventional HSC. A concrete mix with optimum content of ingredients is desired to satisfy the strength and workability. Compressive strength of mix with HF combination of SF and PPF is found to be higher than other mixes. Mix with SF and BF exhibited higher tensile strength. Contribution of fibers was confirmed by SEM analysis.

This investigation exhibits a study on the effect of silica fume, Rice husk ash and Ground granulated blast furnace slag on mechanical property of Performance based concrete. The Performance based concrete with various proportion of different mineral admixtures were tested including compressive strength at 7,14 & 28 days of curing. The ordinary Portland cement by weight was partially replaced with Rice Husk Ash (10%, 15%, 20%), Silica Fume (10%, 15%, 20%) and Ground granulated blast furnace slag (10%, 20%,40%). Estimations were completed subsequent to restoring at 20 °C and 65% relative humidity. Total 90 cubes were casted for different mixes for compressive strength of concrete. The test results reported that optimum % of Rice Husk Ash is for the Mix(C90RHA10) and the compressive strength increases by 6.62% compare to control mix at 28 days. Also, the optimum % of Silica Fume is for the Mix (C80SF20) and the compressive strength increases by 13.4%. Similarly, the optimum % of GGBFS is for the Mix (C60GGBFS40) and the compressive strength increases by 6.81%.

To reduce the carbon foot print from the production of Portland cement, there is requirement of creating other bond produced materials to make concrete. In this connection several efforts are put forward to develop binders with pozzolanic materials without cement, for this addition of chemicals is unavoidable to cause reactive, this work involves the use of fly ash, Recycled aggregate, alkaline activated fluids. Alkaline to binder ratio is 0.55 with exchange of 100% cement with fly ash and determine the strengths for 24hrs oven curing at temperature 60 °C and 28 days atmospheric curing. In this work waste materials fly ash and GGBFS are taken in the proportion of 70:30. The proportion of Sodium Silicate and Sodium Hydroxide is taken as 2.5 and the alkaline liquid to binder ratio is taken as 0.5. The molarity of the alkaline solution is taken as 8 M and 10 M. In this work, the coarse aggregates have been replaced by recycled aggregates for different proportions i.e. 0%, 25%, 50% and 100% the mechanical properties such as compressive strength, Split Tensile and Flexural Strength are evaluated.

The aim of this work was to study the single and combined effects of laboratory synthesised, purified, functionalised multi-walled carbon nanotubes (MWCNTs) and nanosilica (NS) particles on the physico-mechanical and dynamic properties of cement mortars. Portland cement was partially substituted by nanostructured MWCNTs (0.2, 0.4, 0.6, 0.8 and 1.0 wt%), then NS (2, 4, 6, 8 and 10 wt%) and finally both MWCNTs and NS in different ratios. The physico-mechanical and dynamic properties of the composite materials (compressive strength, bending strength, water consumption and initial and final setting times) were measured. The morphology of hardened samples was studied by scanning electron microscopy (SEM) and transmission electron microscopy was conducted to determine the size of the nanoparticles. The results showed that, compared with control samples, the compressive strength of the cement mortars containing MWCNTs increased by 27% at 28 days and the bending strength increased by 9.9% at early age. SEM images showed that the cement mortar containing 0.4 wt% MWCNTs had a more compact microstructure than then the control samples due to the bridging effect of the MWCNTs.

An experimental investigation into the shear behavior of Glass Fiber Reinforced Polymer (GFRP) reinforced concrete beams is presented. The study also looks at the effectiveness of shear strengthening of such beams using externally-bonded Carbon Fiber Reinforced Polymer (EB-CFRP) sheets and investigates the possibility of interaction between internal and externally bonded shear reinforcement. A total of 18 beams, 2.4 m long with a rectangular cross-section of 300x200, reinforced with GFRP bars and stirrups were tested. Three types of concrete were used in this study; ordinary Portland cement (OPC) concrete, Fiber Reinforced concrete (FRC), and Geopolymer concrete (GPC). Six beams, two for each concrete type, severed as control while the other twelve were strengthened using “U” shape EB-CFRP sheets. The CFRP sheets were placed in two different arrangements, above and in-between internal stirrups locations. The results indicate that GFRP is a viable reinforcement for GPC, OPCC, and FRC, whereas EB-CFRP proves to be a feasible strengthening technique for such composite systems. The gain in shear strength for EB-CFRP strips beams on the location of internal stirrups is 5–10% lower as compared to the other arrangement. The difference in the strength gain may indicate a possible interaction between the internal and external shear reinforcement.

Blended cements having partial replacement of fly ash (FA) and granulated blast furnace slag (GBFS) with Ordinary Portland Cement (OPC) have proven to be more sustainable cements with several ecological benefits, increased performance and durability aspects compared to plain OPC. In this study, three blended cements, namely Portland Pozzolana Cement (OPC + FA), Portland Slag Cement (OPC + GBFS) and Composite Cement (OPC + FA + GBFS) are examined. Three Particle Packing Models (PPM) viz. Modified Toufar Model (MTM), J D Dewar model (JDD) and Compressible Packing Model (CPM) are considered to evaluate the gradation of fine aggregates used in designing the mortars and are compared with the mortars designed as per IS 650:2008. The theoretical maximum packing density values obtained based on MTM, JDD and CPM models are 0.681, 0.674 and 0.668 respectively, while the experimental packing density values are 0.617, 0.626 and 0.642 respectively. The compressive strength of Composite Cement (CC), Portland Slag Cement (PSC) and Portland Pozzolana Cement (PPC) mortars exhibited a delay in gain of strength compared to OPC mortars. The mortar samples prepared using CPM model, showed an average increase in compressive strength of 20.71% at 7 days, 12.26% at 28 days and 10.29% at 90 days compared to samples designed using IS 650:2008. Similar trend was observed from MTM and JDD mortar samples also with strength of mortars varying as CPM > MTM > JDD > IS 650. This shows that particle packing models are useful in overcoming the delay in early strength of blended cements due to slow pozzolanic reaction. The hydrated phases of cement and microstructure is examined using Scanning Electron Microscopy and X-Ray Diffraction.

Efflorescence in geopolymers results from mobility of excess alkali and consequent crystallization of alkali carbonates. Efflorescence potential of various geopolymers has been reported previously but the knowledge regarding the effect of efflorescence on the microstructure and mechanical properties of geopolymers remains limited. In this work, metakaolin-based geopolymers were exposed to air, partially immersed in water, and fully immersed, to simulate different processes involved in efflorescence formation. The mechanical properties were assessed by compressive, splitting tensile and flexural strengths, and linear deformation. The microstructural features were investigated by SEM, synchrotron XRD, multinuclear MAS NMR, MIP and synchrotron X-ray microtomography. Extensive efflorescence resulted in a reduction of mechanical strength and changes in the nanostructure and microstructure, which is different from observations for Portland cement-based materials, where efflorescence is usually regarded as a surface or aesthetic problem. The understanding of the relationship between efflorescence formation, the synthesis and exposure conditions provides important insight into the manufacturing and application conditions of geopolymer related materials.

Efforts are being made by several researchers and concrete technologists towards sustainability of concrete. Researchers are working on the replacement of ordinary Portland cement either partly or fully by using mineral admixtures. Geopolymer concrete has been a relatively new development which is becoming popular over the last decade. It is prepared with mineral admixtures, coarse and fine aggregates and certain chemicals so as to undergo polymerization. In the present experimental investigation, the main aim is to develop a more efficient and stronger fiber reinforced geopolymer concrete using several mineral admixtures and fibers so as to recommend it for structural applications. Fiber reinforced geopolymer concrete mixes were produced by employing metallic fibres like steel and non-metallic fibers like glass. Four types of mineral admixtures like fly ash, ground granulated blast furnace slag, condensed silica fume, and metakaolin were mixed in several percentages to serve as the binder. Solidum hydroxide with the required molarity and sodium silicate were used as alkaline liquids for polymerization. Various combinations of fibrous geopolymer concrete mixes by incorporating steel and glass fibers were prepared separately. Specimens were prepared for all the mixes and tested after 28 days of ambient curing for mechanical properties like compression, split tension & flexure. Tests for mechanical properties were conducted on hardened specimens and conclusions are drawn on optimum combinations. From the test results it can be concluded that by reinforcing GPC with fibers strength properties and other benefits can be achieved. The results indicate that fiber reinforced geopolymer concrete may be used for structural applications.

The sustainable utilization of demolition wastes in the production of building materials is regarded as an eco-efficient approach for conserving naturally-occurring resources accompanied by resolving the environmental problems caused by these wastes. Accordingly, the motivation behind this work is evaluating the single and combined effect of nano-waste ceramic (NWC) and nano silica (NS) on the performance of Portland cement concrete. Portland cement was individually replaced by different contents of NWC (2-10 wt. %) and NS (1-4 wt. %). Another mixture was designed to evaluate the synergetic impact of NS and NWC mixture (3 and 6 wt. %) on the performance of concrete. The mechanical (flexural, splitting tensile and compressive strengths) and nondestructive tests (Ultrasonic Pulse Velocity ‘UPV’) were carried on the control and nano-modified hardened concrete. The results showed that the increase of NWC content up to 6wt. % has resulted in a noticeable increment in strengths at all curing ages, followed by a reduction in strengths when NWC content reaches 10 wt. %. However, the usage of 10% NWC illustrates a slight enhancement in strengths compared to control sample. All over the mixtures, the nano-silica modified samples demonstrate a slight enhancement in the mechanical properties compared to NWC. The highest mechanical properties accompanied by the shortest transmitted waves were achieved by the hardened samples having the mixture of 3 wt. % NS and 6 wt. % NWC. This means that the sustainable utilization of NWC not only improves the performance of concrete but also resolves the environmental problems caused by this waste. The sustainable utilization of demolition wastes in the production of building materials is regarded as an eco-efficient approach for conserving naturally-occurring resources accompanied by resolving the environmental problems caused by these wastes. Accordingly, the motivation behind this work is evaluating the single and combined effect of nano-waste ceramic (NWC) and nano silica (NS) on the performance of Portland cement concrete. Portland cement was individually replaced by different contents of NWC (2-10 wt. %) and NS (1-4 wt. %). Another mixture was designed to evaluate the synergetic impact of NS and NWC mixture (3 and 6 wt. %) on the performance of concrete. The mechanical (flexural, splitting tensile and compressive strengths) and nondestructive tests (Ultrasonic Pulse Velocity ‘UPV’) were carried on the control and nano-modified hardened concrete. The results showed that the increase of NWC content up to 6wt. % has resulted in a noticeable increment in strengths at all curing ages, followed by a reduction in strengths when NWC content reaches 10 wt. %. However, the usage of 10% NWC illustrates a slight enhancement in strengths compared to control sample. All over the mixtures, the nano-silica modified samples demonstrate a slight enhancement in the mechanical properties compared to NWC. The highest mechanical properties accompanied by the shortest transmitted waves were achieved by the hardened samples having the mixture of 3 wt. % NS and 6 wt. % NWC. This means that the sustainable utilization of NWC not only improves the performance of concrete but also resolves the environmental problems caused by this waste.

The disposal of waste vehicle tires is an environmental and health problem, as their recycling is very difficult. One of the effective ways of recycling is using these tires as partial replacement of Portland cement in construction industry. In this study, a systematic experimental study (by making 810 laboratory samples) is performed on concrete made with finely ground rubber (GR) and metakaolin (MK) as partial replacements of cement to investigate the compressive strength, splitting tensile strength, flexural strength, water absorption, and dry unit weight. The main goal of this study is to achieve the optimal proportions of concrete incorporating GR and MK by maximizing mechanical strengths while minimizing the water absorption (WA) of concrete. To do so, 7 concrete mixtures containing GR are produced with 3 different cement contents: 350, 400, and 450 kg/m3 in conjunction with 2 different water-cement ratios: 0.45 and 0.50. Also, 1 concrete mix is used to optimize the concrete with hybrid blends of GR and MK by employing the response surface methodology (RSM). GR and MK are applied as partial replacements of Portland cement in ranges of 0–30 vol% and 0–20 vol%, respectively. The results show that the use of GR and MK in concrete has a significant effect on its mechanical and durability properties and, thus, reduces the cement consumption which can contribute to decreasing the negative impacts of cement production on the environment. According to the optimization results, 4.2% and 19.5 vol% replacements of cement with GR and MK, respectively, can be considered as the optimum mixture compositions of hybrid concrete to maximize compressive and splitting tensile strengths by about 1–4% and 6–8%, respectively, while minimizing WA by about 48%. Depending on the flexural strength results, the amounts are changed into 1.8% and 14.7% while the flexural strength increases by about 11%.

Supplementary cementitious materials (SCMs), including industrial by-products or natural pozzolans are widely used as a partial replacement of ordinary Portland cement (OPC) in eco-friendly concrete, to reduce the carbon footprint and enhance mechanical and durability properties. Although many experiments have been conducted to study the effect of SCMs in concrete, the research on the effect of natural pozzolans on fiber reinforced concrete (FRC) is limited. This study investigates the effect of different amounts of metakaolin and zeolite pozzolans on the mechanical properties and durability of concrete containing polypropylene fibers. A total of 99 specimens were made in 11 experimental groups and the parameters of compressive strength, tensile strength, water absorption, porosity and density of concrete specimens were evaluated. In addition, concrete specimens were tested for ultrasonic pulse velocity (UPV) and atomic force microscopy (AFM) to further study the effect of natural pozzolans on the microstructure of concrete. The performance of FRC with natural pozzolans was compared to that of reference concrete and fiber reinforced concrete without SCMs. The results indicated that the polypropylene (PP) fibers were more effective in enhancing mechanical properties of concrete in the zeolite mixtures, so that the compressive strength and tensile strength compared to reference concrete increased by 44 and 22%, respectively, while the water absorption and porosity decreased by 48 and 45%, respectively. This is attributed to the higher viscosity of the zeolite-mixtures that allowed for a better dispersion of fibers in the mixture as well as the improved bond strength between fibers and paste due to the high pozzolanic activity of zeolite. The AFM analysis, UPV, density, and permeable voids test results revealed that the FRC mixtures incorporating natural zeolite had the most dense microstructure and the least porosity and defects among all examined FRC mixtures even compared to the mixtures that incorporated metakaolin with the same cement replacement level.

Geopolymer concrete is considered to be a sustainable alternative to Portland cement in construction industry. The incorporation of nano materials into geopolymer matrix contributes to enhance the mechanical and durability properties of concrete. Carbon nanotubes (CNTs) are characterized by high tensile strength and good durability properties. However, CNTs particles have significant large specific surface area that leads to encounter adhesion and dispersion difficulties in geopolymer matrix. Nano clay (NC) is utilized to increase pozzolanic activity and decrease the adhesion problems in geopolymer concrete. This research aims to investigate the hybrid effect of NC and CNTs on the resulting performances of hybrid fly ash/slag geopolymer concrete. In this study, geopolymer mixes were produced using fly ash/slag as an aluminosilicate source. The utilized alkaline activator was composed of both; sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solutions. Mechanical properties of the mixes were determined based on compressive and flexural strengths tests. Also the impacts of the inclusion of NC and CNTs on the air content, chloride resistance and water penetration depth on hybrid fly ash/slag geopolymer concrete were demonstrated. It was observed that the superior compressive strength for geopolymer mix was found to be in the mix incorporated by (2.5%) NC blended with (0.01%) CNTs. The engineering properties were significantly improved by using hybrid nanoparticles. The high pozzolanic effect of NC led to improve the compressive strength, as long as the nanotubes were used to reinforce the geopolymer concrete and hence enhance the durability properties.

Cellular concrete is a lightweight solid cementitious foam that is used mainly for thermal insulation and sound absorption. Either partially or wholly, when the Portland cement in the binder is replaced with ash, the environmental impact of the material is reduced. However, the resulting changes in the cell structure and their subsequent impact upon the physical properties of the material have not been well examined. In this study, cellular concrete was prepared from alkali activated fly ash binders and separately, from Portland cement binders blended with wood ash. The cell structure was photographed using laser confocal microscopy and the images were analyzed to quantify the cellular network in terms of the porosity and the fractal dimension of the porous phase. Alongside, the cellular concrete specimens were tested for their thermal constants and sound absorption. The results show that there was an increase in the fractal dimension and an associated drop in thermal conductivity for an increase in the porosity.

The traditional cementitious product is prone to suffer from a high degree of deterioration in the case of exposure to acid solutions because of the decomposition of the binder network. However, the degradation of concrete structures in service by mild concentrations of acid under conditions involving sewage, industrial waters, and acid rain is more common and results in a significant environmental problem. The utilization of alkali-activated materials has been seen to potentially offer an attractive option with regard to acceptable durability and a low carbon footprint. With the aid of visual observation, mass loss, compressive strength tests, X-ray diffraction, Fourier transform infrared spectroscopy, and field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, the acid resistance of alkali-activated fly ash mortars in which the precursor was partially replaced (0-30% by mass proportion) with ordinary Portland cement (OPC) was evaluated after 180 days of exposure to mild-concentration sulfuric and acetic solutions (pH = 3). A conventional cement mortar (100% OPC) was used as a reference group. The results demonstrate that the addition of OPC into the alkali-activated system causes a significant increase in compressive strength (around 16.08-36.61%) while showing an opposite influence on durability after acid attack. Based on a linear mean value and nonlinear artificial neural network model simulation, the mass losses of the specimens were evaluated, and the alkali-activated pure-fly ash mortar demonstrated the lowest value (i.e., a maximum of 5.61%) together with the best behavior in the aspect of discreteness at 180 days. The results from microstructure analysis show that the coexistence of the N-A-S-H and C-S-H networks in the blend system occurred by both OPC hydration and FA. However, the formation of the gypsum deposition within the fly ash-OPC blend systems at sulfuric acid was found to impose internal disintegrating stresses, causing a significant area of delamination and cracks. In addition, alkali metal ion leaching, dealumination, as well as the disappearance of some crystalline phases occurred in specimens immersed in both types of acids.

Da mistura de solos com ligantes hidráulicos resultam materiais cimentados artificialmente através de ligações físicas (minerais resultantes da hidratação do ligante). A geometria das ligações é controlada pela quantidade de água usada no processo construtivo que, por sua vez, depende de requisitos de trabalhabilidade e da adição ou não de adjuvantes. Na compactação a quantidade de água é baixa e as ligações tendem a concentrar-se nos contactos entre as partículas, onde a água fica retida num solo não saturado. Na injecção a quantidade de água é alta (assim como a dosagem) e as ligações são dispersas. Discute-se de que forma a geometria das ligações resultante do processo de mistura afecta o comportamento hidro-mecânico de solos arenosos tratados com cimento Portland. Usa-se como exemplo os resultados de ensaios realizados em amostras de uma areia tratada com diferentes dosagens de cimento e relações água/cimento, que permitiram a caracterização do seu comportamento mecânico e hidráulico, e ainda ensaios não destrutivos para caracterização dessas ligações. Observa-se porosidade dupla quando as ligações são concentradas, o que afecta essencialmente as características hidráulicas. As características mecânicas dependem essencialmente da dosagem de cimento, mas a quantidade de água usada também afecta as características da pasta de cimento endurecida.

Cement has been well documented to positively affect the early-age strength of the cement asphalt emulsion mixtures (termed as CAEM) without compromising workability. However, the long-term performance of the CAEM incorporating multiple cement combinations is not conclusive. This study explored the effect of the combined usage of ordinary portland cement (OPC) and sulfoaluminate cement (SAC) on the long-term performance and microstructural properties of a CAEM system in detail. Three tasks were conducted, including (1) designing six CAEM formulations by introducing different types (OPC and SAC) and contents (2–6 wt%) of cement; (2) evaluating the long-term performance by moisture susceptibility, frost damage, abrasion resistance, and rutting resistance; and (3) characterizing the microstructural properties by scanning electron microscopes and energy-dispersive spectrometers. The experimental results revealed that the relative dynamic elastic modulus of CAEM was increased to 69.7% when admixing 90 wt% OPC and 10 wt% SAC. The mixture incorporating 90 wt% OPC and 10 wt% SAC demonstrated excellent rutting resistance up to ~ 31,000 cycles/mm of dynamic stability. The improved long-term performance actually originated from the reduced voids and produced a dense microstructure. The outcomes could facilitate tailoring CEAM products with better long-term performance.

This research focuses on studying the effect of different supplementary cementitious materials (SCMs) such as waste ceramic powder (WCP), lime powder (LP), and ground granulated blast furnace slag (GGBS) in combination on strength characteristics and microstructure of quaternary blended high-strength concrete. To achieve the aims of the study, necessary physical and chemical composition tests were done for the raw materials. Then, mixes were designed into control mix with 100% Ordinary Portland Cement (OPC) and experimental mixes containing 30%, 40%, 50%, and 60% of GGBS, WCP, and LP in combination. Tests were conducted during casting and at curing ages of 7 and 28 days. Accordingly, the control mix which is concrete grade 50 (C-50) as per American Concrete Institute (ACI) mix design is used as a reference for comparison of test results with those specimens produced by partial replacement of SCMs. The characterizations of high-strength concrete are done using consistency, setting time, workability, compressive strength, flexural strength, and morphological tests. The optimum percentage replacement is 50% OPC replacement by 30% GGBS + 10% WCP + 10% LP. Based on the experimental investigations, the workability increases as the replacement level of SCMs increases from 30% to 60% by weight. Compressive strength and flexural strength results increase up to 11.41% and 20% when the percentage replacement increases from 30% to 50% of SCMs replacement at 28 days of curing time, respectively. There are also improvement in the microstructure and significant cost saving due to replacing OPC partially with SCMs with proportions mentioned above. Therefore, the practice of utilizing increased percentage of SCMs in quaternary blend in concrete can be beneficial for the construction industry and sustainability without compromising the quality of the concrete product.

In this study, it is aimed to determine the durability performances of bitumen-modified sulfur polymer concrete (SPC) under the long-term freeze–thaw cycles and to examine the results in comparison with sulfur concrete (SC) and traditional Portland cement concrete (PCC). Three different bitumen ratios were selected as 2.5%, 5%, and 7.5% by weight of pure sulfur for the modification. To check whether the modification was sufficiently realized, the changes in the microstructure of the modified sulfur were examined by a polarized optical microscope, differential scanning calorimetry, and scanning electron microscope. The sulfur modification of the modified sulfur sample prepared with 2.5% bitumen addition among the selected bitumen ratios was successful. Therefore, modified sulfur prepared with this ratio was used in the preparation of SPC. SPC, SC, and PCC prepared with the similar compressive strength were subjected to 150, 300, 450, 600, and 1200 freeze–thaw cycles. After the freeze–thaw cycles, the compressive strength, ultrasonic pulse velocities, relative dynamic modulus of elasticity, and weight changes were examined. At the end of 1200 cycles, the residual compressive strength value in SC and SPC was determined 24% and 58%, while the strength test could not perform on the PCC. SPC, SC, and PCC showed a reduction in RDME 49%, 77%, and 100%, respectively. PCC could not preserve their structural integrity, while the weight loss of SPC was found to be below 1% at the end of 1200 cycles. It was determined that SPC has better durability performance under long-term freeze–thaw effects than SC and PCC.

Carbonated wollastonite clinker (CS) may be suitable as supplementary cementitious material (SCM) for mortar and concrete. The microstructure of unground CS clinker, carbonated CS slurry and a mortar blended with carbonated CS are investigated by scanning electron microscopy. Additionally, a reference mortar with pure Portland cement and one with a cement replacement level of 30 mass-% by carbonated CS are produced to assess its contribution to compressive strength development. The calcium silicates are decalcified during carbonation resulting in CaCO3 and amorphous SiO2 . The latter reacts when used as SCM in mortar influencing the Ca/Si ratio of calcium-silicate-hydrate and contributing to compressive strength development.

High carbon footprint of cement production is the major drawback of plain cement concrete resulting in environmental pollution. Geopolymer composites paste can be effectively used as an alternative to Portland cement in the construction industry for a sustainable environment. The demand for high-performance composites and sustainable construction is increasing day by day. Therefore, the present experimental program has endeavored to investigate the mechanical performance of basalt fiber-reinforced fly ash-based geopolymer pastes with various contents of nano CaCO3. The content of basalt fibers was fixed at 2% by weight for all specimens while the studied contents of nano CaCO3 were 0%, 1%, 2%, and 3%, respectively. The compressive strength, compressive stress-strain response, flexural strength, bending stress-strain response, elastic modulus, toughness modulus, toughness indices, fracture toughness, impact strength, hardness, and microstructural analysis of all four geopolymer composite pastes with varying contents of nano CaCO3 using scanning electron microscopy (SEM) were evaluated. The results revealed that the use of 3% nano CaCO3 in basalt fiber-reinforced geopolymer paste presented the highest values of compressive strength and hardness while the use of 2% nano CaCO3 showed the highest values of flexural strength, impact strength, and fracture toughness of composite paste. The SEM results indicated that the addition of nano CaCO3 improved the microstructure and provided a denser geopolymer paste by refining the interfacial zones and accelerating the geopolymerization reaction.

This research aimed to present the improvement of the cementitious material in high-volume fly ash using only one alkali activator. Fly ash was used as a partial replacement for Portland cement type I, varying from 0 to 60% by weight of the binder. Concentrations of NaOH varying from 0.00 to 1.25 molar were used as alkali activator. Paste properties and mortar compressive strength at the ages of 3, 7, 14, 28, 60, and 90 days of water curing were investigated. The results reveal that fly ash paste with an alkali activator provides shorter initial setting time when compared to control paste without alkali activator. The use of 0.50 molar NaOH concentration in mortar containing fly ash not exceeding 50% by weight of binder provides the highest compressive strength at any age of curing. At that concentration, there is a significant increase in the 28-day compressive strength of up to 45% over that of the control mortar. In addition, higher NaOH concentration (not exceeding 1.00 molar) has a significant positive effect on the compressive strength of mortar with higher fly ash content, especially over longer curing periods.

The aim of this study is to evaluate the usability of new cement (NC) made by the burning of quinary by-product to make commercial binders. Chemical analysis of the by-products and NC as well as X-ray diffraction (XRD) analysis of NC, fineness, density, consistency, and setting time of NC paste, and slump in addition to compressive strength (CS) and splitting tensile strength (STS) of NC concrete (NCC) were conducted. The results suggested that chemical composition of by-products is suitable to make NC binder. The NC contains Ca3SiO5, Ca2SiO5, Ca3Al2O6, and Ca3Al2FeO10. The particles passing through the 200 um Sieve were 56% compared with 52% for Portland cement (PC). The density of the of NC was similar to that of PC. The NC needed 48% more water than PC for normal consistency. The initial and final setting-time of NC was 105 min and 225 min respectively which is much higher than that of PC (15 and 45 min). The slump, compressive strength and splitting tensile strength were slightly lower for concrete containing NC compared with that pf PC concrete. Although the CS and STS of NCC are the lowest, the rate of the CS and STS gain of NCC is greater than that of PCC. It was concluded that NC is a viable alternative to PC for the production of greener concrete. (C) 2021 The Authors. Published by Elsevier B.V.

In this work, a study of the integral strength and deformation characteristics of centrifuged and vibrocentrifuged concretes on activated Portland cement is carried out. Mechanical activation of cement was carried out using a specialized grinding unit. The manufacture of centrifuged and vibrocentrifuged samples was carried out on an experimental laboratory centrifuge. All samples were made from concrete of the same composition. In total, four basic samples of annular cross-section were manufactured and tested with the following dimensions: outer diameter D = 450 mm; inner hole diameter d = 150 mm; total height H = 1200 mm. The optimal values ​​of technological parameters of centrifugation and vibrocentrifugation are given. A scheme has been developed for obtaining small-sized samples from a common annular section to determine the strength and deformation characteristics. According to the results of the study, it was found that an improvement in the values ​​of integral strength and deformation characteristics when using activated Portland cement is observed in both centrifuged and vibrocentrifuged samples. It was found that samples made by vibrocentrifugation technology have the best strength and deformation characteristics than samples made by centrifugation. The conclusion is made about the technology of vibrocentrifugation as the most preferable for the manufacture of reinforced concrete products of annular section.

This study enhances the durability of mortar blends against the combination of chloride and sulfate attack by replacing the certain quantity of Portland cement with microsilica and colloidal nanosilica. Coastal surroundings have severe chloride and sulfate ion precipitation. To establish concrete durability under these environments it is essential to incorporate both ions. Investigation of microsilica and colloidal nanosilica in concrete has been acknowledged in recent times. Moreover, the role of durability mortar combined with microsilica and colloidal nanosilica (CNS) have also been limited. A preliminary tool is conducted to establish five different chlorides and sulfate corrosive solutions to evaluate various replacement percentages of microsilica and colloidal nanosilica content in cement. In binary and ternary solutions, the necessary properties such as mechanical, electrical, change in mass, expansion, permeability and surface morphology were studied. Results revealed that colloidal nanosilica as a partial substitution improved mortar property, enhanced mortar durability and less deterioration in ordinary Portland cement (OPC) specimens and the chloride penetration developed by inserting sulfate ions at an early immersion age.

Cement is the basic material for making concrete that can be used as a hydraulic binder. There are various types of cement including OPC and PCC cement. The problem now is that there is no technical data that can be used as a reference in determining the proportion of the mixture. Examples of cement are obtained from the same factory. namely PT. Semen Tonasa, South Sulawesi with an amount of 78.96 kg of cement for each type of cement. From the results of laboratory tests, it was found that the data on the comparison of concrete using OPC and PCC cements had different data on the of OPC cement is 3.726 Mpa and PCC cement is 3.223 Mpa and for testing the modulus of elasticity of OPC cement is 19371.316 Mpa and PCC cement is 17579.182 Mpa. The test results have met the standard for structural concrete with the same water-cement factor.

Current study explores the possibility of improvement in various categories of concrete’s strengths (including tensile strength, flexural strength etc.) by using methylcellulose as an additive. The effect of methylcellulose on concrete’s compressive strength has also been investigated experimentally. Concrete samples were casted with several methylcellulose to binder ratios varying from 0.002 to 0.01 by weight of cement. Several tests were performed on concrete specimens including concrete cylinder and cube compression tests, split cylinder tests and modulus of rupture tests. Results showed that addition of methylcellulose increased the tensile strength of concrete. Addition of 0.2% of methylcellulose increased the tensile strength of concrete by 16%. This increase in tensile strength reached up to 73% of the control sample on addition of 1% methylcellulose. It was observed that the effect of methylcellulose on compressive strength of concrete depends upon the type of samples being tested (cube or cylinder). The compressive strength of concrete cylinders showed a plateau behavior with peak at 0.4% methylcellulose content with an increase of 18.7%. Effect of methylcellulose on concrete cylinder strength becomes insignificant beyond 0.6%. It was observed that addition of methylcellulose reduces the modulus of rupture values. The reduction in MOR was only 3% at 0.2% methylcellulose content but it grew to 30% at 1% methylcellulose content. The research presents an effective way of increasing tensile strength of concrete but without significant effect on concrete’s compressive strength and modulus of rupture values. These findings can be used to determine optimum content of methylcellulose to achieve desired performance from concrete depending upon the intended use.

In this study, the rheo-viscoelastic behaviors of calcium sulphoaluminate (CSA) modified Portland cement (PC) pastes were investigated. The shear stress, apparent viscosity, frequency sweep and time sweep curves of composite pastes with different PC and CSA volume fractions were analyzed, and the minimum apparent viscosity (ηmin) of PC-CSA pastes were predicted. Results show that with the increase of PC and CSA volume fractions, ηmin, critical strain and flow strain of pastes increase at both 5 min and 60 min resting time, and the phase angle varies under different time spots. The accuracy of viscosity prediction models for 5 min and 60 min are both relatively high. Meanwhile, the reason why the prediction accuracy of 5 min is higher than 60 min is that with the prolongation of resting time, the relationships between particle volume fractions and rheological properties are affected by early microstructure formed by flocs and hydration products, thus affecting their original functional relationship at 5 min.

The environmental impact of traditional Ordinary Portland Cement (OPC) concrete is a significant problem that requires urgent solutions in the construction industry. The development of geopolymer concrete is one of the most significant breakthroughs in the process of replacing OPC concrete. Through comprehensive experimental and numerical analyses, this study investigates the structural behaviours of large-scale steel reinforced geopolymer concrete beams (GCBs) made from low-calcium fly ash and ground granulated blast furnace slag (GGBFS). Firstly, small-scale experiments were carried out to investigate the effects of water/binder and activator/binder ratios on the mechanical properties of geopolymer concrete (e.g. elastic modulus, compressive strength, direct tensile strength). The experimental results show that the mechanical properties of geopolymer concrete increases with increasing the activator/binder ratio and decreasing the water/binder ratio. Secondly, three groups of GCBs with different steel reinforcement ratios (D1-0.41%, D2-0.75%, and D3-1.5%) were made and four-point bending tests were conducted. The same mix proportion (water/binder of 0.45 and activator/binder of 0.08) with the compressive strength of 39.1 MPa, elastic modulus of 32.0 GPa, and the direct tensile strength of 3.06 MPa, was used for the three groups. The obtained moment–curvature results, which consists of three distinct stages (linear elastic, tension cracking of GCBs, and steel yielding), show that the three groups (D1-D3) behave in a ductile manner. Moreover, the moment capacity of GCBs increases when the steel reinforcement ratio increases (D1-21.5 kNm, D2-44.2 kNm and D3-83.6 kNm). Finally, nonlinear, three-dimensional finite element (FE) analysis based on the damage plasticity constitutive law was developed to capture and validate the structural behaviour of GCBs from the experiments. Numerical results indicate that the developed FE models accurately capture the structural behaviours (moment–curvature and cracking behaviour) of GCBs. The discrepancies between the numerical and experimental moment–curvature results are from 1 to 5% for the tensional cracking and yielding points. Therefore, the developed FE models can be used as an effective tool for the further development and design of geopolymer concrete structures.

Introduction. The purpose of the article is to expand the range of compositions for special structures, which will allow them to be operated in extreme conditions. To achieve this goal, a number of tasks have been solved containing ways to improve the efficiency of composites, incl. low-permeability ones. Materials and methods. The research methodology includes a system of transdisciplinary approaches that evaluate the composite as a complex system, taking into account the provisions of geomimetics, such as the law of similarity, the law of affinity of structures, technogenic metasomatism, and micromechanics of composite media. Results. A wide range of cement concretes has been created for unique objects: low-permeability (for protective objects, reservoirs and hydraulic structures). The developed composites have the following performance characteristics (the results for the control sample are given in parentheses): water absorption by weight — 2.5 % (6.1 %), waterproof grade — W14 (W10), air permeability — 0.0253 cm3/s (0.0565 cm3/s), vapor permeability — 0.0021 mg/(m-h-Pa) (0.0030 mg/(m-h-Pa)), effective diffusion coefficient — 1.34 · 10–4 cm2/s (1.56 · 10–4 cm2/s). Conclusions. The similarity in the work of the components of different composite binders, incl. During the two-stage hydration of clinker minerals, in particular, in the first phase, the formation of low-density compounds of different phases occurs, and in the second phase, the binding of calcium hydroxide to low-basic crystalline hydrates occurs. The increase in the activity of the composite binder is due to the synergistic effect of a number of reasons: amorphous silica-containing components bind Ca(OH)2, released during the hydration of clinker minerals, in the second generation CSH(I); limestone particles clog the pores, compacting the structure; and fly ash microspheres are centers of crystallization of new growths.

This study extended blending proportion range of ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement blends, and investigated effects of proportions on setting time, workability, and strength development of OPC-CSA blend-based mixtures. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) were conducted to help understand the performance of OPC-CSA blend-based mixtures. The setting time of the OPC-CSA blends was extended, and the workability was improved with increase of OPC content. Although the early-age strength decreased with increase of OPC content, the strength development was still very fast when the OPC content was lower than 60% due to the rapid formation and accumulation of ettringite. At 2 h, the OPC-CSA blend-based mortars with OPC contents of 0%, 20%, 40%, and 60% achieved the unconfined compressive strength (UCS) of 17.5, 13.9, 9.6, and 5.0 MPa, respectively. The OPC content had a negligible influence on long-term strength. At 90 d, the average UCS of the OPC-CSA blend-based mortars was 39.2 ± 1.7 MPa.

This paper proposes a new type of column. The glass fiber reinforced polymer (GFRP) bar reinforced geopolymer concrete (GPC) filled GFRP tube column is presented as a potential substitute of steel reinforced ordinary Portland cement concrete (OPC) column. Type of concrete (OPC and GPC), type of longitudinal reinforcement bars (steel and GFRP) and type of transverse reinforcement (steel helix and GFRP tube) were the test parameters investigated in this study. The specimens of 200 mm diameter and 800 mm height were tested under different loading conditions. Experimental load-axial deformation, load-lateral deformation and flexural load-midspan deflection of the tested specimens are presented and discussed. An equation was also proposed for the prediction of the concentric load capacity of the column. It was found that GFRP reinforcement and GFRP tube confinement resulted in a higher ductility enhancement for GPC based specimens as compared to the OPC based specimens. Also, the ductility of GFRP bar reinforced GPC or OPC filled GFRP tube columns increased with the load eccentricity. Whereas, the ductility of the steel reinforced specimens decreased with the increase of load eccentricity.

Two types of nanomaterial: Tio2 nanoparticles (NPs) and carbon black NPs have used in this research to study their effect on compressive strength, shrinkage and flow table tests Cement mortar. The mixing ratio was 1:2.7:0.485 (cement, sand, water/cement ratio) for compressive strength test and 1:2 (cement, sand) with the water/cement ratio was a variable value for dry shrinkage test. The two nanoparticles’ ratios are (0.25%, 0.75%, 1.25 % and 1.75%) by weight of the Portland cement. The test results show that the highest value of compressive strength was obtained when using Tio2 at 1.25% wt. of cement. But when using carbon black nanoparticles, the greatest value was obtained when adding it with a ratio of 1.75 % wt. of cement. Using two NPs when added to cement mortar has a negative effect on the shrinkage value.

Nowadays, producing eco-friendly concretes by reducing the usage of high volumes of Portland cement is a global aim. Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) involve using high volumes of Portland cement, which leads to high heat of hydration as well as high carbon emissions that enhance global warming. Therefore, researchers worldwide are interested in producing and assessing Green Ultra-High Performance Fiber Reinforced Concrete (GUHPFRC) which is the main focus of this paper. In this study, thirteen mixtures of such concretes are prepared to study the effect of using Fly Ash (FA) class F, as a Portland cement substitute by volume. The Fly Ash ratios of 15%, 30% and 45% are used to study the effect on the compressive strength of UHPFRC. The paper also focuses on incorporating both corrugated and end hook steel Fibers in the mixes with ratios (1%, 2%, 3% and 4%) to compensate for the decrease in compressive strength of concrete due to the replacement of cement by FA. The results showed that the substitution of 45% of the Portland cement with FA along with the incorporation of steel Fibers in the UHPFRC can be effective without any compressive strength loss.

Recycled aggregates present a varied mineralogical composition and the grading of these particulates over their particle size distribution influence the aggregate properties as well as those of the composites that they form. This study proposed a comparative investigation of the influence of the particle size distribution of fine aggregates from two different origins, namely, natural crushed stone and construction and demolition waste (CDW). Three particle size distributions were defined, so that each aggregate had its fineness modulus (FM) ranked in the granulometric ranges, following the NBR 7211 Brazilian standard. The following tests were carried out: consistency, bulk density in the fresh state, compression strength, absorption (by immersion and capillarity), dimensional and mass variation. The results showed that the aggregate mineralogical composition impacted the mortar properties and that, when analyzed along with the particle size distribution, CDW showed different and varied behavior as a function of its particle size and distribution. Another finding was that mortars produced with CDW aggregate with granulometry below the lower optimal zone (FM

Purpose Recent advances in 3D printing construction elements have focused on ordinary Portland cement (OPC) concrete using polymeric binders; herein, this study aims to produce the same using pure water. Design/methodology/approach A binder jet printer prototype was used to fabricate specimens that are used to assess geometric and mechanical properties. Two distinct water-based binder formulations, compatible with OPC chemistry and piezoelectric jetting device, were used: pure water and water-polyvinyl alcohol (98:2 w/w) solution. Findings This study examines the effect of binder flow rate on dimensional accuracy. Furthermore, the changes in the mechanical properties over time with hydration have been investigated. Practical implications Results indicate that the increase in mechanical strength of Portland cement concrete with pure water was consistent; however, it was delayed by the water: PVA (98:2 w/w) solution. Post-curing by water vapor hardened the structure with the removal of layering native to 3DP and decreased infilling porosity by diffusion mechanism. Originality/value This paper has used pure water jetting for BJT of Portland cement-containing bodies.