Ordinary Portland Concrete Research Articles

Monte Carlo simulation of shielding materials in storage drums for 241Am-Be disused sealed radioactive sources

Disused Sealed Radioactive Sources (DSRS) containing neutron sources such as 241Am-Be require careful management due to neutron radiation. However, finding readily available and effective combination layer shielding materials for practical use to safely contain 241Am-Be can be challenging. The main objective of this study is to investigate the configuration of shielding materials and determine the maximum activity of 241Am-Be sources that can be safely stored in a 200-L drum. A three-layer shielding approach using a 200-L drum as a storage container, with sequential layers of lead (Pb), polyethylene (PE), and ordinary Portland concrete (OPC), achieves the lowest dose rates compared to other combination sequences, as shown by Monte Carlo simulations. With a fixed lead thickness and varying polyethylene and ordinary Portland concrete thicknesses, Monte Carlo simulations using the Particle and Heavy Ion Transport code System (PHITS) demonstrate that this drum design can safely accommodate activities ranging from 22.01 Ci to 72.92 Ci of 241Am-Be. The fitted model equation determines the required polyethylene thickness for any activity within this range. Additionally, case-based simulation results indicate that Indonesia's total inventory of 241Am-Be DSRS can be stored in three 200-L drums with a polyethylene thickness of 15 cm. This configuration meets international standards, ensuring the dose rate does not exceed 2 mSv/h at the surface and 0.1 mSv/h at 1 m from the drum's surface.

Experimental Investigation on Mechanical and Durability Properties of Geopolymer Concrete

Abstract: Geopolymer concrete (GPC) is a new type of concrete that is made with alkaline activators and aluminosilicate materials, such as fly ash and ground granulated blast furnace slag (GGBS). GPC has several advantages over traditional Portland cement concrete (OPC), including higher early strength, better durability, and lower environmental impact. This paper presents an experimental analysis of the mechanical and durability properties of GPC. The mechanical properties investigated include compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity. The results show that GPC has comparable or better mechanical properties than OPC at all ages. GPC also has superior durability properties to OPC, with lower water absorption, higher acid resistance, and lower chloride permeability. The overall findings of this study indicate that GPC is a promising alternative to OPC for a wide range of applications. Since Geopolymer concrete doesn’t use any cement, the production of cement shall be reduced and hence the pollution of atmosphere by the emission of carbon dioxide shall also be minimized. Cement, being a key material of concrete, experiencing a rise in global demand. It has a massive carbon footprint having a contribution of about 8% to the global Carbon dioxide emissions. Geopolymer concrete has a huge potential to replace ordinary Portland concrete. For sustainable construction, GPC reduces the use of cement and finds the alternative of cement for the material's binding property. So, the geopolymer concrete is an alternative to Portland cement concrete and it is a potential material having large commercial value and for sustainable development in Indian construction industries.

Mesoscopic investigation of the matrix pores and ITZ effects on the mechanical properties of seawater sea-sand coral aggregate concrete

In this study, the matrix pores and ITZ effects on the mechanical properties of seawater sea-sand coral aggregate concrete (SSCAC) were investigated via the meso-element equivalent method. The effective modulus and strength of aggregate and matrix in SSCAC at different scale level were derived via the Voigt model and Mori-Tanaka method. A three-step equivalence process was established to consider the influence of the matrix pores. The surface permeability zone for coral aggregate was proposed to explain the strength enhanced effect of the interface transition zone (ITZ) in SSCAC. A comparisons study was carried out to analyze the difference between SSCAC and ordinary Portland concrete about the stress-strain relationships, failure patterns, and failure mechanisms. Finally, the impact of porosity variations on the mechanical properties development of SSCAC have been investigated, which indicate that the compressive and splitting tensile strengths of SSCAC present distinct three-stage variations with respect to porosity. A sensitive range of ITZ effect was proposed to reveal that as porosity within 7%–18%, the variation of porosity can influence the ratio of splitting tensile strength to compressive strength of SSCAC remarkably. To ensure optimal performance in both splitting tensile strength and compressive strength, it is recommended to maintain the porosity of SSCAC within the range of 5%–10%.

Biaxial compressive failure criteria and constitutive model of high-strength geopolymer concrete after high temperature

This paper studies the effect of high temperatures (20℃, 200℃, 400℃, and 600℃) and stress ratios (σ2/σ3) (0.15, 0.3, 0.45, and 0.60) on biaxial compressive strength and strain development patterns of high-strength geopolymer concrete (HGPC). Experimental observations indicate that HGPC exhibits laminar damage similar to ordinary Portland concrete (OPC) before and after exposure to high temperatures, under biaxial compression. Unlike OPC, damage in HGPC initially passes through coarse aggregates at room temperature but shifts predominantly to the aggregate-mortar interface at 600℃. The biaxial compressive strength envelope of HGPC expands with rising temperatures. The increased multiple of biaxial compressive strength (σ3/fm) for HGPC at room temperature rises and then falls with increasing stress ratios, peaking at a stress ratio of 0.45 and surpassing the values for OPC and high-strength concrete (HSC). Before high temperature, the modulus of elasticity of HGPC is higher than that of OPC and decreases with increasing temperature, decreasing by about 45–60% for every 200°C increase, and the reduction is greater than that of OPC. The existing failure criterion is not suitable for HGPC after high temperature, this paper develops a new biaxial compression failure criterion for HGPC before and after high temperature based on Kupfer's criterion, taking into account the effect of temperature. The proposed failure criterion calculation results are well in agreement with the experimental data. A damage constitutive model for HGPC considering the effect of temperature and lateral pressure is also proposed, combining the Weibull distribution model for the ascending branch and a modified empirical model for the descending branch. This combined model effectively predicts the stress-strain relationship of HGPC under various temperature conditions.

Selected Mechanical Properties of Concrete with Regard to the Type of Steel Fibers

Not only in the construction industry, but also in other technical areas, efforts are being made to reduce the costs or difficulty of producing a certain product and at the same time to improve some of its properties. With the development of modern technologies come new possibilities in the development and production of such products. Fiber reinforced concrete is one of them. Fiber reinforced concrete does not fully replace reinforced concrete, but even with a reduction in price and production time, it has a certain part of the properties of reinforced concrete, which can be used for structural elements with specifically required properties. The subject of the presented paper is the testing and comparison of compressive and split tensile strength of steel fiber reinforced concrete (SFRC) with steel fibers MasterFiber 482 with dosage 60 kg/m3 and 90 kg/m3 and SFRC with 5 different types of steel fibers with dosage 50 kg/m3, where dosage 0 kg/m3 represents ordinary portland concrete (OPC). Submitted paper is also focused on specific test methods of concrete, such as measurement of resistance to frost and defrosting chemicals and pressure water seepage.

Comprehensive Analysis of Geopolymer Materials: Properties, Environmental Impacts, and Applications

The advancement of eco-friendly technology in the construction sector has been improving rapidly in the last few years. As a result, multiple building materials were developed, enhanced, and proposed as replacements for some traditional materials. One notable example presents geopolymer as a substitute for ordinary Portland concrete (OPC). The manufacturing process of (OPC) generates CO2 emissions and a high energy demand, both of which contribute to ozone depletion and global warming. The implementation of geopolymer concrete (GPC) technology in the construction sector provides a path to more sustainable growth and a cleaner environment. This is due to geopolymer concrete’s ability to reduce environmental pollutants and reduce the construction industry’s carbon footprint. This is achieved through its unique composition, which typically involves industrial byproducts like fly ash or slag. These materials, rich in silicon and aluminum, react with alkaline solutions to form a binding gel, bypassing the need for the high-energy clinker production required in OPC. The use of such byproducts not only reduces CO2 emissions but also contributes to waste minimization. Additionally, geopolymer offers extra advantages compared to OPC, including improved mechanical strength, enhanced durability, and good stability in acidic and alkaline settings. Such properties make GPC particularly suitable for a range of construction environments, from industrial applications to infrastructure projects exposed to harsh conditions. This paper comprehensively reviews the different characteristics of geopolymers, which include their composition, compressive strength, durability, and curing methods. Furthermore, the environmental impacts related to the manufacturing of geopolymer materials were evaluated through the life-cycle assessment method. The result demonstrated that geopolymer concrete maintains positive environmental impacts due to the fact that it produces fewer carbon dioxide CO2 emissions compared to OPC concrete during its manufacturing; however, geopolymer concrete had some minor negative environmental impacts, including abiotic depletion, human toxicity, freshwater ecotoxicity, terrestrial ecotoxicity, and acidification. These are important considerations for ongoing research aimed at further improving the sustainability of geopolymer concrete. Moreover, it was determined that silicate content, curing temperature, and the proportion of alkaline solution to binder are the major factors significantly influencing the compressive strength of geopolymer concrete. The advancement of geopolymer technology represents not just a stride toward more sustainable construction practices but also paves the way for innovative approaches in the field of building materials.

Mechanical properties and compressive constitutive model of steel fiber-reinforced geopolymer concrete

Geopolymer concrete is an environmentally friendly material, and the addition of steel fibers can overcome its brittleness and improve its performance, which has broad application prospects. However, there are currently few studies on the comparative analysis of mechanical properties between steel fiber-reinforced geopolymer concrete (SFGPC) and steel fiber-reinforced ordinary Portland concrete (SFOPC), as well as uniaxial compressive constitutive models for SFGPC. Therefore, 144 cubes and 36 prisms were tested for SFGPC and SFOPC. The main variables were the volume content of steel fibers (0 %, 0.5 %, 1 %, 1.5 %, and 2 %), curing age (7 and 28 days), and water-to-binder ratio (0.45, 0.5, and 0.55). The slump, failure pattern, compressive strength, splitting tensile strength, elastic modulus, peak strain, toughness index, and compressive stress−strain curves were obtained. The results indicate that with the increase of steel fiber content, the compressive strength, splitting tensile strength, peak strain, and toughness index of SFGPC increase, while the elastic modulus remains almost unchanged. Compared with the plain geopolymer concrete, the above corresponding indexes of SFGPC with 1 % steel fiber content can be increased by 9.9 %, 20.5 %, 23.3 %, and 52.2 %, respectively. The 7-day compressive and tensile strengths of SFGPC can reach about 80 % of the 28-day strengths. Under the same conditions, SFGPC exhibits higher strength, peak strain, and lower elastic modulus than SFOPC. The scanning electron microscope (SEM) test results show that the geopolymer matrix has a denser structure and a tighter bond with steel fibers than the cement matrix. Based on the plain geopolymer concrete, formulas for mechanical indexes and a uniaxial compressive stress−strain model of SFGPC were proposed.

Interfacial debonding mechanism of magnesium phosphate cement onto old concrete substrates under freeze-thaw conditions

The interface created by the repair of damaged ordinary Portland concrete (OPC) structures using magnesium phosphate cement (MPC) is prone to cracking and debonding under freeze-thaw (F-T) conditions and may even cause engineering disasters. In this study, the entire debonding process, moisture migration and debonding mechanism of the MPC-OPC composite interface under F-T actions were investigated and a novel mixed mode fracture criterion was established. The primary findings are drawn as follows: (i) The interfacial crack initiates and propagates along the interface or kinks into the MPC side during F-T actions, depending on the position and thickness of the localized interface F-T damage zone (IFDZ) close to the interface on the MPC side; (ii) The net suction force causes capillary and film water in the mesopores and micropores to migrate to the freezing macropores inside the interface layer, whereas the increase in the liquid pressure caused by the water-ice phase transition causes crack initiation in the macropores and even the interface layer damage; (iii) The stiffness difference between MPC and OPC increases as the molar ratio of magnesia and phosphate (M/P) or the mass ratio of water to cement (W/B) of MPC increases, and the interface debonding mode shifts from propagating along the interface to kinking into the MPC side.

Shear performance degradation of basalt fiber‐reinforced polymer bars in seawater environments: Coupled effects of seawater sea‐sand geopolymer mortar coatings and sustained loading

AbstractGeopolymers, as a promising substitute for ordinary cement, exhibit different coating effects with regard to the durability of basalt fiber‐reinforced polymer (BFRP) bars. In this study, a comparative investigation was carried out on the shear performance of prestressed BFRP bars coated with seawater sea‐sand geopolymer mortar (SSGM). The alkaline content of the SSGM was 4% or 6%. The prestress level was 20% of the ultimate tensile strength at room temperature. The immersion temperatures were room temperature (RT), 40, or 60°C. Interlaminar shear tests and transverse shear tests were conducted at each period (30, 60, 120, and 240 days). The results showed that BFRP bar coated with 6% alkaline content exhibited a slightly higher degradation of shear strength. Furthermore, the prestress developed microcracks in the bars and weakened the interface between the fiber and resin matrix, particular at the elevated temperature. This led to further degradation of the BFRP bars. Additionally, a comparison was made between the shear strength results of BFRP bars coated with SSGM and those coated with ordinary portland concrete or seawater sea‐sand concrete, revealing that the long‐term shear performance of BFRP bars was less negatively impacted by the SSGM coating.Highlights Coupled effects of SSGM coatings and sustained loading on the degradation of BFRP bars are investigated. SSGM provides better protection for BFRP bars than cement‐base concrete. Alkaline content of activator in SSGM has insignificant impact on the BFRP degradation.

Abundant octadecylamine modified epoxy resin for superhydrophobic and durable composite coating

Concretes are generally porous and hydrophilic which lead moisture penetration to corrode metal frame resulting safety concerns. Many attempts to change concrete's wettability were leveraging fluorinated and/or silanized materials that are less environmentally friendly, costly, and non-sustainable. In this study, the epoxy resin and octadecylamine (ODA), two cost effective abundant materials, were combined to form an aqueous hydrophobic slurry as a binder to be mixed into the ordinary Portland concrete (o-concrete). By leveraging the micro/nanostructures in the system, the superhydrophobic concrete composite (SCC) with a water contact angle of 156° and sliding angle of 8° was created. Used as the stucco coating, the SCC exhibited superior adhesion to the o-concrete when hammering and sustained aggressively polishing by sandpapers. In addition, the intrinsic acid and base resistances (pH 1–13) of ODA and epoxy resin have ensured an environmentally stable SCC with an order of magnitude lower current density and 30% higher voltage potential to against corrosions. Furthermore, the SCC had a remarkable self-cleaning ability, and 68% and 87% antimicrobial reductions of Staphylococcus aureus and Escherichia coli bacteria, respectively. Therefore, this s-concrete coating prepared through facile and rapid two-step mixing processes has great potential to be implemented practically in the construction industry.

Microstructural characteristics of bonding interfacial transition zone of concrete and magnesium ammonium phosphate cement

Microstructural characteristics of bonding interfacial transition zone (ITZ) are vital to the bonding performance of new-old concrete, which remains difficult to characterize accurately. In this paper, the microstructural characteristics of ITZ based on magnesium ammonium phosphate cement (MPC) bonding to ordinary Portland concrete (OPC) were investigated by the combination of BSE-EDS and microhardness. It was found that ITZs were distinguished into MPC bonding to OPC paste (ITZ-P) and aggregate (ITZ-A). Meanwhile, Gaussian Kernel Smoothing was suitable to the statistical analysis of microhardness. The peak interval of microhardness in ITZ-P for 113.1 MPa was higher than that in ITZ-A for 87 MPa. It was reflected by the observation of denser hydration products and calculation of lower porosity in ITZ-P, especially the observation of enriched pore area in ITZ-A. Moreover, based on the interrelation of indentation lattice and corresponding distribution of element, the hydration products was quantitatively analyzed. The denser hydration products and lower porosity in ITZ-P are 41.4% and 4.3%, respectively, compared with the 29.3% and 12.5% in ITZ-A. The exposure of more aggregate is not conducive to the attachment of the hydration products of MPC.

Proposition of a methodology for the evaluation of adhesiveness (pull-off test) of aggregate−geopolymer binder interfaces

Portland cement concrete is the most used material in civil construction, but it is a source of greenhouse gases emissions. In addition, its Interfacial Transition Zone (ITZ) is a point of weakness, which limits its performance and application, generating pathological manifestations throughout its service life, decreasing mechanical and durability properties. In this context, geopolymer concretes arise for as a potentially sustainable building material with a much reduced and denser ITZ, when compared to ordinary cement Portland concrete. However, there is a lack of methodology to evaluate the aggregate-geopolymer interface and objectively evaluate compatibility between such new binder and aggregate particles. In other materials, adhesion tests are performed to obtain parameters related to adhesiveness. Provided that context, this work aims to propose a methodology to evaluate the adhesiveness of aggregates and geopolymer binders. For this, a pull-off test based on AASHTO TP 361 (T 361: Standard method of test for determining binder bond strength by means of the binder bond strength (BBS) test, 2022) is proposed, with particular adaptation with respect to specimens’ preparation. The main proposed modifications were: (i) the application method of the binder over a wider surface; and (ii) the use of epoxy glue to attach the pull-off elements (dollies) to ensure the bonding to the geopolymer binder film. Modifications allowed to test the geopolymer adhered to the rock in order to obtain the necessary experimental results. For validation, interfaces composed of a geopolymer binder based on fly ash and steel slag glued onto two granitic rocks (biotite) were prepared and tested. For the test according to AASHTO TP 361 (2022), without the proposed modifications, the adhesion between the geopolymer binder and the equipment proved to be insufficient. Then, with the proposed modified methodology the results were more consistent, in which the specimens showed suitable adhesion for the test. Then, this work contributed to an empirical characterization of adhesiveness for aggregate-geopolymer binder interfaces, enabling adequate analyses regarding the durability, to avoid future pathologies resulting from a weak ITZ and evaluations without huge costs in time and resources.

Corrosion characteristics of tapered sleeve locking-type splicing reinforcement in precast segmental bridge piers

Tapered sleeve locking-type splicing (TSLTS) reinforcement joint is a new type and efficient way of mechanical reinforcement connection, which can be used for connecting of longitudinal steel bars in precast segmental bridge (PSB) piers. Since the TSLTS reinforcement joints are located at the bottom zone of the PSB piers, the PSB piers are often poured with self-compacting concrete (SCC) in this part, which is a new and convenient construction method of PSB piers. In this paper, the corrosion characteristics of TSLTS reinforcement in PSB piers in coastal environment were investigated. Through the accelerated corrosion test, the connection performance of corroded TSLTS reinforcement joints was studied. Then, the corrosion characteristics of TSLTS reinforcement in SCC segment and ordinary Portland concrete (OPC) segment of the PSB piers were discussed, and effect of the interface between the two segments on the corrosion of TSLTS reinforcement was analyzed. The results showed that the critical mass loss for slip failure of TSLTS reinforcement joints was about 7.2%. The mean mass loss of TSLTS reinforcement in SCC segment was larger than that of TSLTS reinforcement in OPC segment, and the corrosion rate of TSLTS reinforcement joints in SCC segment was about 1.54 times that of TSLTS reinforcement in OPC segment. The uneven corrosion coefficient of the TSLTS reinforcement joint was the largest, which increased first and then decreased with the increase of corrosion time. The uneven corrosion coefficient of TSLTS reinforcement in SCC segment was approximately equal to that of in OPC segment, and the uneven corrosion degree of the TSLTS reinforcement joint was about 1.98 times that of TSLTS reinforcement in SCC segment. The mean mass loss of TSLTS reinforcement at the interface was greater than those of in SCC and OPC segments, and the pitting corrosion of TSLTS reinforcement at the interface was more serious. However, with the increase of corrosion time, the uneven corrosion coefficient of TSLTS reinforcement at the interface tended to be equal to those of TSLTS reinforcement at other parts (except the joint). The research results can provide references for the popularization and application of the TSLTS reinforcement joints in PSB piers in coastal environment.

Study of Carbonation-depth Prediction of Unsaturated Concrete Considering Carbonation-produced Water

Carbon dioxide can react with alkaline carbonate substances in cement-based materials, which harms the durability of the concrete structure. The carbonation reaction is a process of releasing water, resulting in an increase in pore water saturation, which was always neglected by previous studies. In this paper, a transient pore water saturation equation is proposed and introduced into the classical carbonation reaction kinetic model, which is simulated by finite-element software with a typical ordinary Portland cement. The model was verified by two classical empirical equations for carbonation-depth prediction. The simulation results indicated that the increment of pore water saturation originated by carbonation-produced water will weaken the CO2 diffusivity and enhance the carbonation resistance. Besides, the growth rate of carbonation depth is slightly faster without considering the produced water and with higher initial saturation, the difference will be more significant. If the influence of carbonation water is ignored, the predicted carbonation depth of unsaturated concrete may be less accurate. This study can provide some reference for theoretical and experimental studies on concrete carbonation. However, future work is still needed including more realistic effects in the model such as the mesoscale modeling of concrete and the integration of stress states. KEYWORDS: Ordinary Portland concrete, Carbonization reaction, Carbon-dioxide transport, Finite-element method, Pore saturation.

Effect of glass powder on the mechanical and drying shrinkage of glass-fiber-reinforced cementitious composites

Ordinary Portland concrete (OPC) is characterized by low tensile strength and low toughness. These properties can be improved by adding glass fiber (GF). However, the alkaline environment of the pore solutions adversely affects the durability of GF. First, the effect of GF addition on the mechanical properties and fluidity of cement mortar was investigated. It was found that the fluidity decreased, and the flexural strength increased with an increase in the GF content. The incorporation of GF had little effect on the compressive strength of mortar. The optimal volume dosage of GF was 2 %. Then, Experiments were conducted to study the effects of glass powder (GP) characterized by different particle sizes and dosages on the fluidity, mechanical properties, and strength activity index (SAI) of glass-fiber-reinforced cementitious composites (GFRC). The results revealed that the fluidity, flexural strength, and compressive strength of GFRC containing GP increased with a decrease in the GP particle size. The flexural and compressive strength of GFRC first increased and then decreased with an increase in the GP content. The SAIs values of all GFRC specimens were more than 75 %, except GPI-25. Finally, the effect of the GPIV (GP of the optimal particle sizes) content on the drying shrinkage and pore structure of GFRC was studied. It was observed that the addition of GP into GFRC resulted in a reduction in the drying shrinkage, and the drying shrinkage of GFRC decreased with an increase in the GPIV content. The pore volume (0.5–50 nm) of GFRC decreased with an increase in the GPIV content. GP in GFRC consumed calcium hydroxide (CH) to produce calcium silicate gel. This helped reduce the extent of corrosion of GF by CH. Waste glass is processed into GP and added into mortar or concrete to replace parts of cement to reduce cement consumption and carbon dioxide emission. This helps protect the environment. GP is a promising agent for the fabrication of glass-fiber-reinforced cementitious composites.

Comparison study on the impact compression mechanical properties of coral aggregate concrete and ordinary Portland concrete

Coral aggregate concrete (CAC) has been widely used in the construction of South Sea islands and reefs. However, the dynamic mechanical properties of CAC under high strain rate loading are rarely reported. This study aims to compares the mechanical properties of CAC and ordinary Portland cement concrete (OPC). A 100 mm-diameter split Hopkinson pressure bar (SHPB) was used to perform an impact compression loading test on CAC and OPC. The dynamic mechanical properties of CAC were assessed in terms of the failure pattern, particle evolution after failure, dynamic increase factor (DIF), brittleness analyses and impact toughness. The results show that the failure plane of CAC directly penetrates the coral aggregate, unlike OPC, which has an interfacial transition zone (ITZ). When the strain rate reaches 166 s−1, the evolution of the particle size after CAC breaks basically becomes stable compared with that after OPC breaks. Under the same strain rate, the DIF value of CAC is higher than that of OPC. An empirical equation is proposed for the estimation of the DIF of CAC based on the experimental results. A significant influence of the strain rate on the dynamic elastic modulus of CAC was observed. Moreover, a method for evaluating the brittleness of concrete under dynamic loading is proposed. At a strain rate of 10-5-166 s−1, comparing with OPC materials shows that there is an obvious brittle-ductile transition in CAC materials. The impact toughness of CAC is significantly lower than that of OPC, and the energy absorbed by CAC before crushing is significantly less than that absorbed by OPC.

Bonding Performance of Steel Rebar Coated with Ultra-High-Performance Concrete

In this study, to improve the bond performance of reinforcing bars fixed inside concrete, a pullout test using ultra high-performance concrete (UHPC) and structural steel fibers was conducted and a model that could predict the performance was also presented. After creating a UHPC layer on the rebar surface, the specimens were prepared along with three types of structural fibers. The structural fibers with different shapes were mixed up to 0.2%, 0,4%, 0.6%, 0.8%, 1% and 2% to analyze their effects on the bond failure at the interface. As a result of the experiment, the pullout resistance ability of the specimen thinly coated with UHPC maintained high residual stress due to the steep section reaching the maximum load, increased the maximum pullout load, and delayed the bond failure during the extraction process. As a result of the cross-sectional examination of the specimen, the coating of UHPC was strongly attached to the rebar surface and the bond surface was broken through sliding at the interface (UHPC–ordinary Portland concrete (OPC)). It was found that the increase in the structural fiber significantly improved the pulling-out resistance at the interface. The proposed model based on the existing Cosenz–Manfredi–Realfonzo (CMR) and Bertero–Popov–Eligehausen (BPE) prediction models was found to be in good agreement with the experimental results.

Engineering properties of geopolymer concrete: a review

Geopolymer concrete (GPC) could be a solution that uses a cementless binder and recycled materials for producing concrete, while reducing the carbon dioxide emission and the demand for raw materials. In addition to the environmental aspect, previous studies on GPC showed that it can achieve mechanical characteristics higher than those of ordinary Portland concrete (OPC) such as greater strength a few days after casting, and it can be suitable for structural applications. In this paper, the state-of-the-art review of GPC is presented through an extensive literature analysis to determine the most recent information regarding the engineering properties of geopolymer concrete and the critical issues that prevent its widespread use and to put forward suggestions for future research. In particular, the physical properties in both fresh and hardened states and the mechanical characteristics are investigated; the structural performance of geopolymer concrete elements is also outlined.

Effect of Curing Regime on Compressive Strength of Geopolymer Concrete

Advancement of reasonable development materials has been the focal point of exploration globally in recent times. Considering the current scenario, finding options in contrast to Ordinary Portland concrete (OPC) is of incredible importance as a result of high CO2 emission during its production. Accordingly, supplementary material was acquainted as alternative to cement for concrete production. Utilisation of fly ash is eco-accommodating and furthermore saves cement cost. It is wealthy in silicate and alumina and it responds with alkaline solution to produce alumina silicate gel which helps in fastening the concrete ingredients. The fly ash based geo polymer offers better protection from the forceful condition and elevated temperature than the ordinary cement. Some factors like NaOH Molarity, NaOH/Na2SiO3 percentage assume a fundamental element in the development of the geopolymerization reaction became concept of. The investigation on the fly ash based geo polymer profoundly did in the present work, besides the impact of elevated temperature and time are not exceptionally recorded in the available literature. In this study the effect of curing temperature and curing time on the compressive strength (3, 7 and 28 days) of GPC at a constant molarity of NaOH and alkaline solution ratio and compare with controlled concrete. In the present work 10 molars of NaOH and 1:1.5 alkaline solution ratio was considered by varying curing temperature 60°, 90° and 120° C and 24, 48 and 72 hours of curing time. M30 grade concrete mix with the equivalent GPC is developed. From the experimental results, it was found that compressive strength was effected by curing temperature and curing time at 3, 7 and 28 days and maximum compressive strength i.e., 53.46 MPa was obtained at higher curing temperature (120° C) and lower curing time (24 hrs). Also, when compared with control concrete, the compressive strength is higher for GPC was observed.

Flexural performance of reinforced Alkali-activated concrete beams incorporating steel and structural Macro synthetic polypropylene fiber

Lately, alkali-activated concrete (AAC) has gained attention due to the environmental impact that Ordinary Portland Concrete (OPC) possesses and durability issues. This paper investigates the flexural behavior of reinforced AAC beams adding 1.5% structural macro synthetic polypropylene fiber and 5% hooked end steel fiber structural, including control. The fiber addition was relevant to the total binder weight. Six beams of 100 mm × 200 mm × 1200 mm beams reinforced with two steel bars of 12 mm in diameter were cast and tested under a four-point loading test. This study evaluated the cracking moment, ultimate load, mid-span deflection, energy absorption, toughness, displacement ductility, failure mode, and crack patterns at yielding and ultimate capacity. The addition of fibers, especially steel fibers, significantly increased the flexural capacity. The steel fiber addition to the AAC beam specimen showed remarkable failure mode. It disturbed the crack pattern due to the fiber action that acted as a bridge controlling the crack propagation and transferring stress from the AAC to the steel fibers. Also, this study evaluated several codes and guidelines provisions in terms of flexural capacity and deflection. The ACI 318 showed conservative predictions rather than ECP 203 and EN 1992–1. Furthermore, a finite element model (FEM) using “ANSYS” was developed and validated. The FEM results provided a good agreement with the experimental results.