Lightweight Geopolymer Research Articles

Development of new material for geopolymer lightweight cellular concrete and its cementing mechanism

Lightweight cellular concrete (LCC) is widely used in engineering and construction because of its low density and good thermal and acoustic insulation capabilities. However, cement production, the cementitious material for LCC, consumes much energy and emits large amounts of CO2. Therefore, reducing cement consumption is one of the main hot issues in the development of China's construction industry. The geopolymer cementitious material is one of the ideal substitutes for silicate cement because of its low energy consumption in production and its ability to give full play to the fly ash and slag activity under the action of alkali excitation. It is imperative to combine geopolymer with LCC to find a kind of lightweight and high strength building material, but there is still a lack of systematic research on this aspect. On the basis of exploring samples of geopolymer lightweight cellular concrete (GLCC), the influence of fly ash, slag content, sodium silicate modulus, alkali content, water cement ratio and other factors on the strength and fluidity of GLCC was analyzed by single factor (SF) test, and the reasonable value range of four factors was proposed. The significant effect of the four factors and the best matching ratio was derived through response surface (RS) test, and RS optimization prediction and validation were carried out. On the other hand, the cementing mechanism of geopolymer on LCC was analyzed from a microscopic perspective by comparing LCC and LCC filled with fly ash (LCCFFA) specimens with SEM tests.

Recycling of Waste Glass in Lightweight Geopolymer Using Iba as a Foaming Agent: Towards Energy Conservation

Recycling of Waste Glass in Lightweight Geopolymer Using Iba as a Foaming Agent: Towards Energy Conservation

Studies on Lightweight Geopolymer Concrete

The studies on Lightweight Geopolymer concrete (LGC) are leading-edge in the development of sustainable and eco-friendly concrete. Attempts were being made to develop LGC by various methods of production. This paper reviews about previously published research work on lightweight geopolymer concrete and the observations to the material binders - an alternate to the Ordinary Portland Cement (OPC) by the utilization of industrial by-products, alkaline activator solution, foaming agents, chemical expansive agents, lightweight aggregate, production methods, and their physical and mechanical properties. The main focus is to investigate pore size formation, density, compressive strength and curing conditions. From the review it is found that the stabilization of foam and the control of efflorescence are the two challenging problems faced by the industry for the mass production of lightweight geopolymer foam concrete. Furthermore, topics for future work in this field were suggested.

Experimental investigation on mechanical behavior of geopolymer light weight concrete

Experimental investigation on mechanical behavior of geopolymer light weight concrete

Physical characteristics and mechanical properties of a sustainable lightweight geopolymer based self-compacting concrete with expanded clay aggregates

Geopolymer Concrete (GPC) is a unique and sustainable building material that has the potential to be transformed into a self-compacted lightweight composite for industrial applications. This paper investigates the sustainability of self-compactable lightweight geopolymer concrete (SCLGC) made from Expanded Clay Aggregate (ECA) to further explore this front. In this study, the physical properties of SCLGC, such as slump flow test, T500 test, V-funnel, and J-ring tests, are examined. Furthermore, the density, Ultrasonic Pulse Velocity (UPV), compressive strength, splitting tensile strength, and impact resistance are also tested to evaluate the mechanical properties of SCLGC mix with various concentrations of Sodium Hydroxide (SH) cured under different curing regimes. The aforenoted properties are examined following the American, Indian and European guidelines. In addition, microstructural analysis is conducted to assess the compactness and internal structure of SCLGC blends with varying SH concentrations cured under different curing regimes. Finally, the sustainability aspects of GPC and SCLGC mixes are analyzed through the Life Cycle Assessment (LCA) and Environmental Impact Assessment (EIA) to evaluate the energy requirement and CO2 emission and cost. The Sustainability analysis was performed to evaluate the energy requirement and CO2 emission of SCLGC in the production of 1 m3 concrete based on the previous literatures. The significance of the proposed research work emphasizes the utilization of ECA as an aggregate material for the development of SCLGC. The cost, carbon and energy efficiency of the SCLGC's mixes were estimated. Mix with ECA requires higher energy demand and emits high CO2 in the open atmosphere. Based on the present analysis it can be concluded that an increase in the concentration of activator solution increases the energy demand and emits more amount of CO2. The inference from the present study reveals ECA can be employed for the production of SCLGC with the replacement percentage not exceeding 50%.

Green materials for construction industry from Italian volcanic quarry scraps

Italian volcanic quarry scraps, with fine particle size and of little market interest, have been considered for the manufacturing of lightweight geopolymers and highly porous foams. Both powders have been alkali activated with NaOH solution at 8 M and 3 M, respectively.Geopolymers were characterized in terms of density, porosity, humidity absorption/desorption, mechanical strength and microstructure. All samples (with a bulk density of 1.5–1.6 g/cm3) exhibited a porosity of approximatively 35 vol% but featured a quite variable compressive strength (3–7 MPa), depending on the use of pumice or lapillus. The same quarry scraps were easily converted into highly porous foams (porosity of 75 vol%), by intensive mechanical stirring of alkali-activated suspensions, with the help of a surfactant.

Static and dynamic properties of novel ambient-cured lightweight geopolymer composites with fibre reinforced epoxy coated EPS aggregates

Geopolymer is an alternative binder to ordinary Portland cement (OPC) and expanded polystyrene (EPS) has been used as lightweight aggregates (LWA) to manufacture lightweight geopolymer composites (LWGC). Nevertheless, incorporating EPS beads in LWGC resulted in a significant decrease in mechanical properties as reported in a previous study. To achieve LWGC with a higher strength-to-weight ratio, a new commercially available coated expanded polystyrene (CEPS) with fibre reinforced epoxy was used as LWA for mixing LWGC in this study. Quasi-static and dynamic tests of the developed LWGC were conducted by using the universal test machine and Ø100-mm split Hopkinson pressure bar (SHPB) system, respectively. The physical properties of LWGC, such as density, workability and microstructure, were reported first, followed by the quasi-static mechanical properties including compressive and splitting tensile strength, modulus of elasticity and Poisson's ratio. Then the failure processes and failure modes observed in dynamic compressive and splitting tensile tests were reported and discussed. The strain rate effects on the dynamic properties, including the compressive and splitting tensile strengths, compressive critical strain and modulus of elasticity of LWGC with various CEPS contents, were revealed. The energy absorption capacities of the tested specimens were also examined. Furthermore, empirical formulae were proposed to predict the dynamic increase factors of both the compressive and splitting tensile strengths as well as energy absorption capacities of LWGC.

Properties of fly ash-based lightweight-geopolymer mortars containing perlite aggregates: Mechanical, microstructure, and thermal conductivity coefficient

It is known that studies on lightweight geopolymer using fly ash need more research. Therefore, in this study, class F fly ash-based lightweight geopolymer mortar samples were produced by using river sand, raw perlite, and expanded perlite as aggregates. The study was planned in two groups. In the first group, river sand, raw perlite, and expanded perlite were used as aggregates. In the second group, raw perlite and expanded perlite were used as aggregates. Expanded perlite replacement rates in both groups were determined as 0%, 20%, 40%, 60%, 80%, and 100%. The produced geopolymer mortar samples were cured at 75 °C for 24 and 48 h. After heat curing, unit weight, ultrasonic pulse velocity, water absorption, porosity, thermal conductivity coefficient, and flexural and compressive strength tests were performed on the samples. In addition, the elevated temperature resistance of the geopolymer mortar samples was tested at 300 °C, 600 °C, and 900 °C temperatures. Moreover, the microstructures of geopolymer mortar samples before and after elevated temperature were examined using a field emission scanning electron microscope. According to the results obtained, with the use of raw and expanded perlite, unit weight, UPV, flexural and compressive strengths of geopolymer mortar samples decreased, while water absorption and porosity increased. Using raw and expanded perlite resulted in an increase in the thermal insulation performance of the geopolymer mortar samples. Furthermore, the use of expanded perlite in geopolymer mortar samples increased the strength of geopolymer mortar samples exposed to elevated temperatures of 900 °C.

Properties and Durability Performance of Lightweight Fly Ash Based Geopolymer Composites Incorporating Expanded Polystyrene and Expanded Perlite

In this study, the use of expanded polystyrene and expanded perlite as lightweight aggregates for the preparation of lightweight geopolymers is tested. The geopolymers’ performance was evaluated through physical, mechanical and thermal testing. Polypropylene fibers were used as reinforcement agents, while the long-term durability was assessed though repeated wet–dry and freeze–thaw cycles and sorptivity tests. The results showed that the introduction of lightweight aggregates in the geopolymer mixes decreased the compressive and flexural strength of the specimens by 77% and 35%, respectively. However, the density and thermal conductivity were substantially improved because of the addition of low-density aggregates. The fiber reinforcement of lightweight samples led to a drastic increase in flexural strength by 65%, leaving unaffected the compressive strength and density of the specimens. The freeze–thaw and sorptivity tests were also improved after the introduction of both aggregates and fibers. Lightweight geopolymer composites exhibiting density in the range of 1.0–1.6 g/cm3, compressive strength of 10–33 MPa, flexural strength of 1.8–6.3 MPa, thermal conductivity of 0.29–0.42 W/mK, and sorptivity of 0.031–0.056 mm/min0.5 were prepared.

Hybrid effect of carbon nanotubes and basalt fibers on mechanical, durability, and microstructure properties of lightweight geopolymer concretes

In this research, a combination of basalt fibers (BFs) and carbon nanotubes (CNTs) were used to improve the engineering attributes of lightweight geopolymer concrete (LWGC). A combination of ground granulated blast furnace slag (GGBFS) and CNTs was utilized as the binder. The experiments consisted of slump, equilibrium density, compressive and splitting tensile strengths, ultrasonic pulse velocity, water absorption, water penetration depth, electrical resistivity, fourier-transform infrared spectroscopy, energy dispersive X-ray microanalysis, and scanning electron microscope. Also, reinforced LWGC beams containing different percentages of BFs and CNTs were fabricated and subjected to four-point loading. The experimental outcomes demonstrated that CNTs could be used as a replacement for a part of GGBFS to obtain structural LWGC with suitable mechanical and durability attributes. The combined use of CNTs and BFs increases the compressive and splitting tensile strength by 32.2% and 43.7%, respectively. Due to greater participation in the geopolymerization process and the formation of hydrated gels, mixes containing CNTs fill the voids and form a dense and cohesive structure. Moreover, the presence of BFs in the binder texture of LWGC strengthens the bond between the binder and the aggregates and prevents the development of capillary cracks. It was observed that the reinforced LWGC beam containing BFs and CNTs had higher flexural strength and better ductile performance than the control specimen.

Effect of high temperatures on the properties of lightweight geopolymer concrete based fly ash and glass powder mixtures

Given the large manufacturing and consumption of concrete globally, there has been widespread speculation that it is a significant source of greenhouse gas emissions. Consequently, scientists are looking for sustainable and beneficial solutions to the environment. The influence of adding expanded clays (Leca) and crushed recycled bricks clay lightweight aggregates (RBA) on the fly ash and glass powder-based geopolymer concrete were investigated at ambient and high temperatures. High temperature influences the significant characteristics of mortar and lightweight aggregate geopolymer concrete. Low calcium fly ash was utilized as a binder in the concrete paste with a 10% replacement rate of Glass Powder. The concrete specimens were heated to 200, 400, 550, and 800 °C at a 7 °C/min rate for 60 min. Lower coarse aggregate strength is a contributing factor to concrete compressive strength reductions. The influences of high temperatures on geopolymer concrete were studied in terms of mass loss, cracking, water absorption, and microstructure. The research outcomes show that the geopolymer concrete suffered damage and dehydration at a heating temperature of 550 °C and above. Acceptable correlation between the temperature degree and Ultrasonic Pulse Velocity UPV with the compressive strength of the lightweight concrete. The test results showed the residual compressive strength 110.2%, 92.9%, 71.9%, and 55.6% as well as 109.2%, 91.5%, 79.6%, and 52.6% in addition to the density reduced 0.17%, 2.56%, 7.29%, and 12.18%, and 0.74%, 3.97%, 6.31%, and 13.25% in 200,400,550, and 800 °C for Leca and RBA type respectively. The equations showed acceptable results with experimental data. The impact of replacing waste glass powder with fly ash on the development of microstructures and gels was also investigated.

Durability of lightweight oil-well geopolymer system in sulfate environment

Sulfates when present in the formation water would attack and deteriorate the cementitious system. In the quest to investigate the possibility of using geopolymer systems in oil-well cementing, the durability of geopolymer in various corrosive environments has been simulated. Lightweight geopolymer systems exhibit different microstructural and macroscopic properties compared to the conventional geopolymer systems whose durability under sulfate attack has been widely investigated. It is therefore important to study the resistance of lightweight geopolymer to sulfate attack. A ternary geopolymer was formulated at 13 ppg (1.56 g/cm3) by admixing metakaolin, ground granulated blast furnace slag (GGBFS), and silica fume in an alkaline solution composed of sodium silicate and 10 M sodium hydroxide solution in a mass ratio 1:3. The geopolymer specimen was cured in a water bath at 163 °F for 72 h and subsequently submerged in a 50 g/L sodium sulfate solution for up to 2 days. The effect of the sulfate solution on the strength and the mechanism of the sulfate attack was analyzed using analytical techniques, pH, and ion exchange measurements. The compressive strength of the specimen at 72 h, having a value of 802 psi decreased by 19.8% and 26.2% after day 1 and day 2 in the sodium sulfate solution, respectively. Investigation of the mechanism indicated that the loss in strength was not a result of the formation of deleterious phases but rather the leaching of Na ions from the geopolymer indicated by the rise in the pH and amount of Na ions in the sodium sulfate solution after the geopolymer was submerged in a sulfate solution. Lightweight geopolymer has a relatively loose microstructure that reduces its tendency to inhibit the transport of alkalis during sulfate attack, making the effect of the sulfate environment more pronounced.

Pelletization and properties of artificial lightweight geopolymer aggregates (GPA): One-part vs. two-part geopolymer techniques

Pelletization is currently the most-widely adopted method for the production of artificial geopolymer aggregates (GPA). However, as a newly-developed technology, there is still lack of fundamental research relevant to the influence of the pelletization techniques on the properties of the produced GPA. In this study, different alkalinity, precursor types and pelletization methods (i.e., one-part and two-part) for GPA production were investigated. Results showed that the pelletization efficiencies of almost all the mixes reached approximately 80%. In terms of GPA properties, the one-part GPA with the alkali concentration of 6% had lower oven-dried particle densities [1851 kg/m3 for highly-reactive fly ash (HRFA) and 1668 kg/m3 for lowly-reactive fly ash (LRFA)] than those of the corresponding two-part GPA (1905 kg/m3 for HRFA and 1705 kg/m3 for LRFA), and higher alkalinity (8%) would result in an even lower oven-dried particle density (1802 kg/m3 for HRFA) when one-part pelletization method was used. It was also found that the one-part GPA had a lower pellet strength than the two-part ones, due to the higher porosity observed in the XCT images. From the internal porosity of GPA in different XCT scanning layers, the two-part GPA showed a more uniform distribution of internal porosity compared with the one-part ones, indicating that the two-part pelletization process is more suitable for GPA production. Given the same alkali concentration (6%), the porosities of two-part GPA (1.0% for HRFA and 1.7% for LRFA) were lower than those of the one-part GPA (3.4% for HRFA and 3.2% for LRFA). The findings of this study can provide useful knowledge for the future industrialization of the pelletization technique in the GPA production.

The Durability of Lightweight Geopolymer Concrete (LGC) on Chloride Resistance

Lightweight geopolymer concrete is an innovative concrete from a combination of environmental-friendly geopolymer concrete and lightweight concrete which has a density of less than 2,400 kg/m³. This concrete does not use Ordinary Portland Cement (OPC) but uses type F fly ash which has the same main composition as OPC namely silica and aluminum. Reducing the use of OPC aims to reduce the production of CO₂ gas emissions which are the main contributors to global warming. This study aims to provide the information needed to develop lightweight geopolymer concrete to reduce carbon emissions and create environmental-friendly concrete materials. The constituent materials of lightweight geopolymer concrete include type F fly ash as precursors, Na₂SiO₃ and NaOH 14 M as activators, fine aggregates in the form of sand as concrete fillers, superplasticizers, and foam. The use of foam helps in reducing the density of lightweight geopolymer concrete. The ratio used in this study is 1:2 for activators and precursors, 1:2 for precursors and fine aggregates, 2.5:1 for Na₂SiO₃ and 14 M NaOH, and 1:40 for foam agents and water with a percentage of foam that is 50% of test object volume. The amount of plasticizer used is 3% of the weight of the precursor. Treatment of the lightweight geopolymer concrete using an oven with a temperature of 60°C for 24 hours and then the specimen coated with plastic wrap for 28 days to achieve maximum compressive strength. Curing for 28 days, the specimen has a compressive strength of 27.9 MPa with a specific gravity of 1,702.5 kg/m³. This research focuses on the durability of lightweight geopolymer concrete using 5% HCl acid solution under different conditions, which are left at room temperature, fully immersed in 5% HCl acid solution, and cyclic conditions. Tests were carried out on days 28 and 56 with observations of changes in compressive strength, density, visual conditions, Scanning Electron Microscope, and XRD. The results showed that acid solutions' long duration and soaking conditions, especially hydrochloric acid, affect lightweight geopolymer concrete.

Study on the Light Weight Geopolymer Concrete Made of Recycled Aggregates from Lightweight Blocks

Abstract: This study studied the properties of lightweight geopolymer concrete that contained recycled lightweight block aggregate. The recovered blocks are classified as coarse aggregates after being crushed.To reduce greenhouse gas emissions, geopolymers have the potential to be used to create new, environmentally beneficial materials. A new class of building materials called geopolymer concrete (GPC) has a replacement for regular Portland cement concrete (OPCC) and are capable of revolution in the construction sector. The impact of On the strength characteristics, alkaline activators have been investigated. Used fly ash was obtained for this study from a nearby thermal power plant. Samples were produced from low-calcium fly ash through activation with a combination of sodium silicate solution and sodium hydroxide. Fly ash was added to the concrete with a ratio of 0.5. Using a mix proportion and 5,10,15 Molar of sodium hydroxide solution, geopolymer specimens were cast. The samples underwent compression testing. test with ambient temperatures for curing. From the analysis ofLiterature suggests that the combination of the aforementioned ingredients is healing. FromAccording to a review of the literature, the amalgamation of the aforementioned elementshas a favorable effect on the strength properties of geopolymer concrete. Since fly ash is viewed as a waste product, geopolymer concrete made from low-calcium fly ash costs less than Portland cement concrete as a result. Lowcalcium fly ash-based geopolymer concrete has good compressive strength, very little drying shrinkage and minimum creep, great resistance to sulphate attack, and superior acid resistance.

Behavior of bond-slip relationship of lightweight and normal weight geopolymer with various FRP sheets using end-groove anchorage

In this study, the effect of using an end-groove anchorage system (EGA) on the bond-slip behavior between fiber-reinforced polymer (FRP) sheets and both normal weight geopolymer (NWG) and lightweight geopolymer (LWG) concrete was investigated by considering the effects of different types of FRP sheets (CFRP, BFRP, and GFRP), FRP bonding lengths of 50 and 100 mm, FRP bonding widths of 50 and 75 mm, and with and without an EGA system. A total of 96 specimens of NWG and LWG concrete were cast, bonded with FRP sheetsand tested under double-shear tension. The results of employing EGA revealed that the bond-slip behavior of NWG specimens differed from that of LWG specimens. Using the EGA system significantly enhanced the bond force by an average of 16 % and 18 % for NWG and LWG, respectively. However, the ultimate slippage of NWG specimens was reduced by as high as 60 % as a result of using the EGA system, but it contributed to increasing the ultimate slippage remarkably by as high as 73 % for LWG concrete specimens. It's worth noting that the bond-slip behavior of CFRP sheet outperformed all other types of FRP sheets for both NWG and LWG concrete. The type of geopolymer concrete, the kind of FRP sheets, and the EGA process all influence specimen failure modes. The EGA system was more favorable for the bond failure of CFRP sheet and NWG concrete specimens, resulting in the avoidance of sudden debonding of CFRP composite and block contacts. A bond-slip model was proposed in this study to predict specimen bond force and slippage. The model was well fitted to the experimental data and appeared to have potential as a practical application which is the first and only model in the literature in this field.

Geopolymer Concrete with Lightweight Artificial Aggregates.

This article presents the physical and mechanical properties of geopolymer concrete with lightweight artificial aggregate. A research experiment where the influence of fly ash–slag mix (FA-S), as part of a pozzolanic additive, on the properties of geopolymers was carried out and the most favorable molar concentration of sodium hydroxide solution was determined. The values of three variables of the examined properties of the geopolymer lightweight concrete (GLC) were adopted: X1—the content of the pozzolanic additives with fly ash + flay ash–slag (FA + FA-S) mix: 200, 400 and 600 kg/m3; X2—the total amount of FA-S in the pozzolanic additives: 0, 50 and 100%; X3—the molarity of the activator NaOH: (8, 10 and 12 M). In order to increase the adhesion of the lightweight artificial aggregate to the geopolymer matrix, the impregnation of the NaOH solution was used. Based on the obtained results for the GLC’s compressive strength after 28 days, water absorption, dry and saturated density and thermal conductivity index, it was found that the most favorable parameters were obtained with 400 kg/m3 of pozzolanic additives (with 50% FA-S and 50% FA) and 10 NaOH molarity. Changes in the activator’s concentration from 8 to 10 M improved the compressive strength by 54% (for a pozzolana content of 200 kg/m3) and by 26% (for a pozzolana content of 600 kg/m3). The increase in the content of pozzolanic additives from 200 to 400 kg/m3 resulted in a decrease in water absorption from 23% to 18%. The highest conductivity coefficient, equal to 0.463 W/m·K, was determined, where the largest amount of pozzolanic additives and the least lightweight aggregate were added. The structural tests used scanning electron microscopy analysis, and the beneficial effect of impregnating the artificial aggregate with NaOH solution was proved. It resulted in a compact interfacial transition zone (ITZ) between the lightweight aggregate and the geopolymer matrix because of the chemical composition (e.g., silica amount), the silica content and the alkali presoaking process.

Residual mechanical performance of lightweight fiber-reinforced geopolymer mortar composites incorporating expanded clay after elevated temperatures

This research provides an experimental investigation on the properties of fiber reinforced composite materials consisting of lightweight expanded clay aggregates (LECA) and polyvinyl alcohol (PVA) fibers. The influence of temperature (room temperature, 250°C, and 500°C) on the lightweight geopolymer mortar (LWGM) composite materials is also explored. LECA is used as a partial replacement to river sand with 60% and 80%. The base material utilized for LWGM is slag activated by a mixture of sodium silicate and sodium hydroxide solutions. The fresh properties in terms of workability and density were performed. A series of experiments, such as compression, flexural and uniaxial tensile strength tests, were executed to assess the mechanical properties of LWGM composite materials. In addition, the microscopic variations due to the elevated temperature were also evaluated by scanning electron microscopy (SEM) to understand the macro-scale behavior of the samples. The results indicated that increasing the level of LECA replacement caused a reduction in the density and compressive strength of the LWGM. Also, incorporating a 1% PVA fiber volume fraction significantly enhanced the flexural and uniaxial tensile behavior of LWGM composite materials. The compressive strength enhancements were observed at 250°C due to further geopolymerization, while compressive strength reductions were obtained at 500°C due to the vapor impact and difference in thermal expansion. In addition, the load-carrying capacity of all samples increased, and displacement capacity decreased under flexural tests at 250°C. However, the ductile behavior of the PVA incorporating specimens changed to brittle due to the melting of PVA fibers.

Effects of hybrid fibers and nanosilica on mechanical and durability properties of lightweight engineered geopolymer composites subjected to cyclic loading and heating–cooling cycles

This paper discusses the influence of nanosilica and hybrid fibers on the mechanical behavior and microstructure of fly ash and slag-based lightweight geopolymer composites exposed to 0, 10, 20, and 30 heating–cooling cycles. Nanosilica (NS), polypropylene (PP), and polyvinyl alcohol (PVA) fibers 2% by volume raction were used to enhance lightweight engineered geopolymer composites (EGC). Prior to and beyond heat cycles, the flowability, density, mass loss, scanning electron microscopy (SEM), and residual mechanical characteristics (static and cyclic loading responses, tensile stress, strain capacity, and load–deflection response) were evaluated. The experimental findings revealed that adding 2%NS, 2%PP fiber, and 2%PVA fiber into lightweight EGC composites enhanced compressive strength by 4.75%, 13.59%, and 27.14%, respectively, at room temperature. Thermal cycles increased the compressive strength of nanosilica and PVA fiber samples by 12.41% and 21.67%, respectively. After 30 heat cycles, the samples reinforced with PP fibers lost 20.26% of their compressive strength. Since tensile characteristics were much more sensitive to the development of internal microstructure deficiencies during thermal treatment, the tensile stress and strain capacity of all lightweight EGC specimens dramatically reduced and lost their strain hardening behavior after being exposed to new heating–cooling cycles. The microstructural analysis of the hybrid system indicated that the bonding characteristics between both the EGC matrix and the PP fibers were weak, and the PP fibers had a negligible influence on the ductility properties of the hybrid composite as compared to using just PVA and PP fibers. PVA fibers did not melt after being subjected to various heating–cooling cycles at 200 °C, but PP fibers melted entirely during thermal cycles, and the lightweight EGC microstructure revealed apparent faults such as micro-cracks and a significant number of capillaries.

The effect of scoria, perlite and crumb rubber aggregates on the fresh and mechanical properties of geopolymer concrete

To broaden the practical applications of the geopolymer concrete (GC) at the same large-scale structural level as the conventional concrete (CC), careful assessment of the fresh and mechanical performance of the new concrete technologies based on the GC binder are essential. Lightweight concrete (LWC) is of significant importance for the seismic-resistant lightweight structures, while rubberised concrete is an innovative structural material to tackle the issues associated with the accumulation of the scrap tires in the environment. Current research makes attempt to develop and characterise the rubberised geopolymer concrete (RGC) using 10-mm recycled crumb rubber (CR) aggregates as substitution for the natural coarse aggregates by 5, 10, 15, and 20% replacement. Lightweight geopolymer concrete (LWGC) utilising lightweight scoria and perlite aggregates as replacement for the natural coarse and fine aggregates, respectively, by 25, 50, 75, and 100% proportions were prepared as well. Thereafter, the RGCs and LWGCs were subjected to the fresh and mechanical properties analysis after 3, 7, and 28 days of ambient-curing. For the RGCs, the obtained results denoted no deterioration of the flowability, improved 7-, and 28-day compressive, tensile, and flexural strengths, and enhanced strain-hardening behaviour comparing to the plain GC. For the LWGCs, the obtained results revealed severe segregation for the mixes containing 25% perlite or more, and high risk of segregation for the mixes containing more than 75% scoria. The results obtained for the mechanical properties of the LWGCs suggested that the scoria content in the range of 25–75% improved the fresh and mechanical properties of LWGC compared with GC. In addition, the RGCs represented superior load-bearing capability rather than the LWGCs.