Residual Compressive Strength Research Articles

Microstructural and Residual Properties of Self-Compacting Concrete Containing Waste Copper Slag as Fine Aggregate Exposed to Ambient and Elevated Temperatures

In recent times, with rapid development in the construction sector, the use of enormous amounts of materials is required for the production of concrete. Fire penetrates concrete, leading to chemical contamination, small cracks, and lightening. These effects can significantly change the properties of concrete’s structure, reduce its strength and durability, and also change the behavior of the structure and lead to effects on the environment. An attempt was made to study the effects of elevated temperature on the mechanical characteristics of self-compacting concrete (SCC) with by-products including fly ash as a partial replacement for cement and waste copper slag as a partial replacement for fine aggregate at 0%, 10%, 20%, 30%, 40%, 50%, 60%, and 70%. The SCC specimens were subjected to elevated temperatures ranging from 200, 400, 600, and 800 °C, respectively, for a steady-state of two hours in a digital muffle furnace. The residual compressive strength, mass loss, ultrasonic pulse velocity, and residual density along with a visual inspection of cracks and color changes were observed. In this study, with over 400 °C temperatures, surface fractures appeared. The residual compressive strength (R-CMS) of all the individual temperatures of the SCC-WCS% mixes exhibited a gain in strength range from 31 to 34 MPa at 400 °C, 26 to 35 MPa at 600 °C, and 22.5 MPa to 33.5 MPa at 800 °C, respectively. Microstructural analysis of SCC-WCS% mixtures subjected to elevated ambient temperatures is carried out with a scanning electron microscope (SEM) and X-ray diffraction (XRD).

Utilizing bio-based and industrial waste aggregates to improve mechanical properties and thermal insulation in lightweight foamed macro polypropylene fibre-reinforced concrete

This research intends to examine the potential of incorporating waste materials in place of coarse aggregates to augment the mechanical characteristics and thermal insulation of lightweight foamed concrete (LWFC), along with the inclusion of polypropylene (PP) fibres. The PP fibre exhibits excellent tensile strength and enhancement on thermal insulation properties of cementitious materials. In this study, eco-friendly bio-based oil palm shell (OPS) and robust solid polyurethane (SPU) aggregates derived from industrial waste were utilized as substitutes for conventional aggregates. Additionally, silica fume was partially incorporated as supplementary cementitious materials. The addition of PP fibre impacted the workability of the LWFC with the inverted slump value decreased by 1.7 %–17.5 %. The inclusion of PP fibre proportion increased from 0 % to 0.5 % revealed a positive result in mechanical properties and thermal insulation performance. The OPSSPU/0.5 showed the significantly increment of 40.4 % compressive strength, 102.9 % of splitting tensile strength, and 70.8 % flexural strength, respectively. The optimum result was obtained in the OPSSPU/0.5 mixture, which exhibited 3.74 MPa residual compressive strength. Furthermore, utilizing PP fibres brought about a significant reduction in thermal conductivity in the environmentally sustainable LWFC, leading to improvements ranging from 0.2 % to 16.3 % when compared to the control composition. Thus, these findings are essential for encouraging the adoption of such practices in the construction industry and contributing to the reduction of environmental impacts associated with sustainable concrete production.

Fire Resistance of Lightweight Aggregate Concrete Containing Spent Garnet as Partial Fine Aggregate Replacement

Introduction The escalating demand for concrete, driven by global infrastructure development, poses significant challenges to environmental sustainability due to the depletion of natural resources and the accumulation of waste materials. This paper explores the potential of utilizing waste materials, particularly palm oil clinker (POC) and spent garnets, as sustainable alternatives in concrete production. The depletion of natural aggregates, such as river sand, coupled with the environmental hazards associated with waste disposal, underscores the urgent need for eco-friendly solutions in construction materials. POC, derived from palm oil production waste, and spent garnets from abrasive industries offer promising avenues for reducing environmental impact and enhancing sustainability in concrete production. By addressing the dual challenges of resource depletion and waste management, this research aims to contribute to developing greener construction practices and mitigating environmental degradation. Aims This study aims to investigate the effects of incorporating spent garnet as a partial fine aggregate replacement on the fire resistance of POC LWAC. By examining the interplay between spent garnet inclusion and fire resistance, the research contributes to developing more sustainable concrete formulations and aids in industrial waste management practices, addressing critical societal and environmental challenges. Methods This study investigates the effects of elevated temperatures on the compressive strength and durability of POC LWAC specimens. Concrete specimens were demoulded after 24 hours of curing and submerged in water for 28 days. Compressive strength and water absorption tests were conducted at the end of the curing period. Subsequently, specimens were subjected to temperatures of 300 °C, 500 °C, and 700 °C for 1 hour in a furnace. After cooling naturally for 24 hours, visual inspection, mass reduction analysis, and evaluation of residual compressive strength were performed. Results Results indicate that 20% garnet replacement yields the highest compressive strength due to pore filling and denser structure. Higher garnet levels lead to reduced strength and increased water absorption. Visual assessment post-heating shows surface alterations, with 20% garnet exhibiting the lowest mass loss and strength reduction at elevated temperatures. Conclusion Notably, specimens containing 20% spent garnet in POC LWAC performed better in a fire than others, enhancing their fire-resistant properties. In summary, this research introduces a hopeful approach to improve the sustainability of concrete and mitigate the environmental repercussions of industrial waste.

Compression and hydrothermal ageing after impact of carbon fibre reinforced epoxy laminates

This paper proposes a new methodology for the assessment of seawater ageing effects on impact-damaged composite laminates. CF/Epoxy laminates which were unimpacted, and impacted at 30 J, 60 J, and 90 J by hemispherical and conical impactors were subject to 4 months hydrothermal ageing in renewed natural seawater at 60 +/-2 °C. The majority of water uptake by impacted laminates (0.05 wt% − 0.3 wt%) occurred in the first 24 h and is believed to be held in damage cavities by capillary mechanisms. The increase in diffusive water uptake rate by the matrix due to impact damage was only small, at less than 0.008 wt%.mm.hr−0,5, compared with the total diffusive water uptake rate of 0.1 wt%.mm.hr−0,5. Hydrothermal ageing reduced the residual compressive strength of pristine laminates by 25 % and impact-damaged laminates by 8 % to 16 % for impacts between 30 J and 90 J.

Exploring the flowability, physical, and mechanical properties of eco-friendly colored cement mortars with metakaolin under sulfuric (H2SO4) and nitric acid (HNO3) attacks

This article aims to investigate the flowability, physical, mechanical, and durability properties of metakaolin (MK)-added colored cement mortars exposed to the effects of H2SO4 sulfuric acid (SA) and HNO3 nitric acid (NA). MK was used in 20 % replacement with cement, and yellow (YP) and red pigments (RP) were added to the mixtures at 1 % and 3 % of the cement by weight. According to the results, although MK reduced the workability and, therefore, the flow diameter (FD) of mortars, thanks to the void-filling feature of MK, filling the voids in the microstructure caused the samples' apparent porosity (AP) and relative dynamic modulus of elasticity (RDME) to decrease. Additionally, MK significantly improved the residual compressive (RCS) and residual flexural strengths (RFS) of the samples thanks to the calcium-silicate-hydrate (C–S–H) bonds it formed in the interior structure, owing to its high pozzolanic efficiency. Moreover, this improvement of MK is more remarkable in samples that remain subject to SA and NA attacks for more time.Furthermore, while YP reduces the workability of mortars and, therefore, the FD value due to its needle-tipped grain structure, RP increases the FD value of the mortars with its spherical grain structure. However, YP and RP contributed to reducing the AP of the samples and increasing RCS and RFS capacities at a meager rate by showing a micro-filling effect. In addition, there were significant increases in the total color changes (ΔE) of YP and RP-added colored mortar samples, especially after longer SA and NA attacks.

Effects of silica fume and rice husk ash contents on engineering properties and high-temperature resistance of slag-based prepacked geopolymers

Geopolymer slurries can be favored to achieve a sustainable approach in prepacked aggregate concretes. This study presented here investigated experimentally the effect of silica fume (SF) and rice husk ash (RHA) on the high-temperature resistance of slag-based sustainable prepacked geopolymers. In the production of prepacked aggregate geopolymers (PAGs), ground granulated blast furnace slag (GGBFS) was utilized as the main aluminosilicate-rich precursor material, and SF and RHA were replaced with GGBFS in various contents including 7.5% and 15%. The physical, mechanical and microstructural properties of specimens cured at 35°C and 70°C for 8 hours were determined comparatively. Residual compressive strength and mass loss of mixtures exposed to elevated temperatures (150°C, 300°C, and 600°C) were determined to observe high-temperature effects. The results revealed that the properties of PAGs were affected considerably by curing temperature and precursor type. The maximum oven-dry density of 2244 kg/m3 with RHA content of 7.5% was obtained at 70˚C curing temperature. Specimens produced with RHA tended to absorb more water under both heat curing conditions and the highest water absorption of 10.2% with RHA content of 7.5% was obtained at 35˚C curing temperature. The compressive strength of PAGs varied between 13.7 and 28.10 MPa, and flexural strengths varied between 1.48 and 2.74 MPa. Increasing curing temperature improved the strength properties of PAGs, and in general, the 8-hour compressive and flexural strength values of SF samples were relatively higher. The application of elevated temperature to the PAG mixtures caused a significant reduction in both compressive strength and mass loss. Among the specimens cured at 35°C, the specimens with RHA showed relatively better high-temperature performance in terms of compressive strength, while the specimens with SF cured at 70°C showed better performance. PAG specimens produced with RHA showed the best high-temperature performance against mass loss. According to the results obtained in the given study, these recycled wastes could be used to improve the physico-mechanical properties and high-temperature performance of slag-based PAGs.

Novel thermoplastic matrix resin with low processing temperature and good interfacial strength for carbon fiber-reinforced polyethersulfone

Owing to the increased demand for carbon fiber-reinforced thermoplastic composites with excellent recyclability, there is a need to improve the interfacial bonding between the fiber and matrix. Hydroxy-functionalized polyethersulfone (PES), i.e., PES-OH, and epoxy resin (ER) were included to impart functionality to PES. A mixture of PES, PES-OH, and ERs with a weight ratio of 8:1:1 reduced the Tg by −18% compared with 100% PES. The enhancement of the interfacial properties increased the interlaminar shear, tensile, compressive, and residual compressive strengths by 50%, 22%, 43%, and 25%, respectively. This study can contribute to the development of carbon fiber composites for future mobility.

Experimental Investigation on Partial Replacement of Cement by Granite Powder on Mortar

This paper intends to investigate the possibility of producing low costs enhanced mortar by Granite powder. By taking the enormous amount of cement, it affects the environment badly and demand for cement was increasing day by day. So, by partially replacing Granite powder with cement in construction field. It can fulfill the objectives of catering to the needs of the construction sector while simultaneously promoting an eco-friendly and pristine atmosphere. Partial replacement of cement by using granite powder in mortar gives sufficient strength. The conventional mortar mix consists of cement, fine aggregate, and water. In this experimental study granite powder was used with different percentage, such as 20% 25%, 30% 35%. The mixture was prepared and mortar cubes were made and allowed for curing. It is concluded that, he immersion of cement mortar in magnesium sulphate is better when compared to sodium sulphate and the sulphate attack is lesser in magnesium sulphate. The residual compression strength for the cement mortar in the proportion of granite content 30% is higher.

Evaluation of freeze-thaw resistance of geopolymer concrete incorporating GFRP waste powder

This study investigates the use of glass fiber reinforced polymer (GFRP) waste powder as a partial replacement for cementitious materials in the synthesis of geopolymer concretes (GPCs), focusing on their durability under freeze-thaw (F-T) conditions. Two types of binary GPCs were synthesized: GFRP powder/ground granulated blast furnace slag (GGBS)-based GPC and GFRP powder/fly ash (FA)-based GPC, with a GFRP powder weight content of 30 %. Single GFRP powder-based, GGBS-based and FA-based GPCs were prepared as reference materials. The F-T resistance was evaluated through mass loss and residual compressive strength (RCS), as well as examining the microstructure using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). Results demonstrated that the mass loss of all GPC samples remained below the critical value of 5 % after 300 cycles. The incorporation of 30 wt% GFRP powder into GGBS-based GPC resulted in improved resistance to F-T damage, increasing the number of cycles endured from 200 to 300. Similarly, adding 30 wt% GFRP powder to FA-based GPC demonstrated enhanced resistance to F-T deterioration, with the number of cycles increasing from 150 to 175. The pore distributions of GFRP powder/FA-based GPC remained relatively unchanged before 200 F-T cycles, indicating it effective resistance against F-T conditions. GFRP powder/GGBS-based GPC exhibited a more uniform and denser microstructure with a reduced presence of pores, even after enduring 300 F-T cycles, making it better equipped to withstand F-T cycles. Furthermore, prediction models were developed to estimate RCS and damage evolution due to F-T conditions, producing accurate results compared to test data. This study presents an effective method for the utilization of GFRP waste as a building material in cold environments.

Exploring nanoscale metallic multilayer Ta/Cu films: Structure and some insights on deformation and strengthening mechanisms

Nanoscale metallic multilayer (NMM) films are systems offering insight into the role of interfaces in metal plasticity, deformation, and strengthening mechanisms. Magnetron sputtering was used to fabricate the Ta/Cu NMM films with a periodicity (equal Ta and Cu layer thickness) from 6 to 80 nm, and with the structure exhibiting immiscible tetragonal β-Ta and face-centred cubic Cu phases. Transmission electron microscopy and X-ray diffraction analyses revealed that, irrespective of the period, all films manifested a polycrystalline structure. The growth direction of both Cu and Ta layers was found to be along 〈001〉 β-Ta || 〈111〉 Cu directions, with the crystallite size constrained by the layer thickness. The studies showed that the Ta/Cu NMMs exhibited compressive residual macro-stress and flow strength, and enhanced elastic recovery at the periodicity of ≤12 nm. Activation volume V⁎ value of 11 to 20 b3 as determined from the indentation creep test under a constant load, may indicate a mixed deformation mechanism. This mechanism likely involves the emission of dislocations from the incoherent Ta/Cu interfaces, as well as the formation of screw dislocations within Cu grains. The high-load indentation test, TEM studies, and the rCLS model collectively demonstrate that all NMM films predominantly undergo plastic deformation. This plastic deformation primarily occurs within the soft Cu layer, while the propagation of dislocations across the incoherent interface is largely excluded.

Bond shear modulus in reinforced concrete at high temperature: A design‐oriented approach

AbstractModeling bond behavior in either ordinary or high‐temperature conditions requires the knowledge of bond shear modulus—called also slip modulus or simply bond stiffness—that has received so far scanty attention because of the greater interest for bond as a guarantee of equilibrium at the Ultimate Limit State (and in fire conditions) than as a means to guarantee both equilibrium and compatibility at the Serviceability Limit State (and in fire/post‐fire conditions). The limited knowledge of bond shear modulus makes it difficult to numerically model such phenomena as tension stiffening, that controls the structural behavior in both ordinary and fire conditions. The general trends identified by examining eleven experimental campaigns with anchored bars covering 27 different cases and temperatures ranging between 20 and 800°C are the starting point of the design‐oriented laws proposed in this study about bond shear modulus as a function of concrete residual strength and temperature. A simple shear‐lag model is introduced for bond shear modulus at room temperature, as its evaluation from test data is no simple matter due to initial chemical adhesion and different test procedures. Bond shear modulus is shown to be a decreasing function of concrete residual compressive strength and of the maximum temperature reached by the bar‐concrete system. Design charts are proposed to allow the designer to identify the value of the bond stiffness on the basis of the max. temperature, of concrete residual strength and of bar diameter, making it possible to realistically model tension stiffening in fire‐damaged RC structures.

Enhanced freeze-thaw resilience of cement mortars through Nano-SiO2 and single/hybrid basalt fiber incorporation: Assessing workability, strength, durability

This study investigated how freeze-thaw cycles (FTC) impact concrete durability and structural integrity, exploring novel approaches like integrating nanomaterials and fibers into concrete compositions. After subjecting the materials to FTC, the study evaluated mortars enriched with nano-SiO2 (NS) and micro- and macro-basalt (BA) fibers. NS was incorporated by substituting 1 % and 2 % of the cement content. Meanwhile, 24 mm in length macro-BA fibers were added individually or in hybrid compositions with 6 mm micro-BA fibers at 0.5 % and 1 % volumetric ratios. The results revealed significant improvements in both the strength and durability of mortar specimens post-FTC, attributed to the enhancing properties of NS. Its capacity to fill voids and substantial pozzolanic activity notably improved the material's performance. However, adding BA fibers adversely affected mortar workability, causing a decrease in flow diameters (FD) as the fiber ratio increased.Nevertheless, BA fibers effectively maintained specimen integrity post-FTC despite leading to decreased residual compressive (RCS) and flexural strengths (RFS). This reduction was linked to the robust bonding between BA fibers and the matrix, impeding crack propagation post-FTC. Interestingly, combining BA fibers in hybrid configurations improved workability and significantly enhanced residual strength characteristics, surpassing singular applications. For instance, after 180 FTC, the K0 control specimen exhibited a 34.17 % and 34.56 % reduction in RCS and RFS, respectively. In contrast, the K10 specimen with 2 % NS and a hybrid combination of BA fibers at a volumetric ratio of 1 % displayed notably lower reduction rates of 23.69 % and 16.99 %, respectively.

Preference of curing regimes based on fire resistance of ultra-high performance cementitious materials (UHPCM) mixed with fly ash

The cement-fly ash (FA) binary system was prepared as the ultra-high performance cementitious materials (UHPCM), and the effect of curing regimes on the evolution of microstructure and compressive strength of UHPCM at elevated temperatures was investigated. The results showed that multi-stage combined curing (MC) could remarkably improve the compressive strength of UHPCM at ambient temperature, which attributed to the further hydration of cement and the pozzolanic reaction of FA to produce more stable hydrates. However, steam curing (90 °C for 7 d) was more conducive to the residual compressive strength growth and retention of UHPCM exposed to elevated temperatures. The mechanism of this phenomenon was revealed by XRD and SEM analysis. The further hydration and conversion reactions occurred mainly inside the steam cured specimens when exposed to fire temperature, and a large number of C–S–H gels were gradually transformed into crystalline hydrates with high strength, excellent thermal stability and different forms, which made the microstructure denser and thus had better fire resistance. Comparatively, a large number of crystalline hydrates were generated prematurely in dry-hot air cured specimens, which made the decomposition reactions dominate under fire, resulting in coarsening of microstructure and reduction of macroscopic mechanical strength of UHPCM continuously.

Effects of elevated temperature exposure on the mechanical properties of recycled fine aggregate concrete

ABSTRACT In this work, a compound waste material was made up of raw construction waste concrete, waste tiles, and waste bricks was mixed at a weight ratio of 6:3:1. They were ground into recycled fine aggregates (RFA). RFA substituted the local river sand in proportions of 0%, 30%, 50%, 70%, and 100% for preparing recycled fine aggregate concrete (RFAC) with varied water-to-cement ratios. It intended to explore concrete’s mechanical properties and ultrasonic pulse velocity changes before and after high temperatures (300–800°C). The loss on ignition (LOI) of concrete was simultaneously determined to compare the performance in resisting elevated temperature. Test results presented that the higher the replacement ratio of RFA, the gradually higher the reduction in the concrete splitting tensile, compressive, and residual compressive strengths and ultrasonic pulse velocity after elevated temperature exposure. A rapid reduction was especially found at the heated temperature of exceeding 440°C. Furthermore, the old cement paste adhered to the surface of the raw construction waste had a relatively higher LOI. This led to the consequence that the RFAC had an increased LOI with the increment of the RFA replacement ratio, while the LOI of RFAC dropped with the increment of the originally heated temperature.

Impact of thermal loads on silica fume-modified lightweight concrete: Machine learning approach to assess compressive strength evolution

Fire resistance of concrete is complex to comprehend as it is a composite material with ingredients of varied thermal properties. As the behaviour of concrete subjected to thermal loads is complex and required exhaustive experimentation, the use of soft computing techniques can be beneficial for predicting the residual compressive strength of concrete. Leveraging the power of machine learning (ML), specifically Artificial Neural Network (ANN), Random Forest (RF), and AdaBoost (AdB) models, this study aims to overcome the limitations of conventional prediction methods. Models were developed for the prediction of residual compressive strength of light weight concrete with silica fume (SF) exposed to thermal loads. Cement, silica fume, lightweight pumice aggregate, water-to-cement ratio, superplasticizer, and temperature were taken as input attributes while residual compressive strength was taken as output. Firstly, the data were subjected to extensive statistical analysis before the models were created. Additionally, hyperparameter tuning using grid search was done to increase the models' efficiency. The coefficient of determination (R2), root mean squared error (RMSE), and mean absolute error (MAE) as model evaluation parameters were used to evaluate the performance of various developed ML models. When the performance of models was compared, it was found that the AdaBoost (AdB) model outperformed all other ML models. Hence, this study highlights the significance of ML techniques in addressing complex engineering challenges and underscore the practical implications for optimizing structural design and performance.

Compressive residual strength of the pultruded glass-fiber composite after tension-compression fatigue

We experimentally determined the decrease of residual compressive strength of the pultruded glass-fiber laminate after tension-compression cyclic loading. The adapted Arcan rig was used for tension-compression fatigue tests. The cyclic load was applied with the critical stress ratio R=−0.87. The residual compressive strength was determined after applying the predefined number of loading cycles with the stress amplitudes of 242 MPa and 173 MPa. The results indicated that the residual compressive strength was reduced about 20% at 77% of fatigue life under the stress amplitude of 242 MPa and at 83% of fatigue life under the stress amplitude of 173 MPa. The microstructural analysis showed that the crack growth path and failure mode depend on the stress amplitude.

Valorization of engineered biochar to develop ultra-high-performance fiber-reinforced concrete with low carbon emission

This research introduces an innovative approach to developing carbon-negative Ultra-High-Performance fiber-reinforced Concrete (UHPC) by incorporating substantial quantities of biochar, both as a binder and as an aggregate, replacing up to 25% by weight of Ordinary Portland Cement (OPC) and quartz sand (QS). The study examines the impact of biochar on cement hydration processes, microstructure evolution, and various other performance metrics in the modified UHPC. Samples were formulated with 3% double-hooked steel fibers and biochar quantities ranging from 5 to 25% by weight as substitutes for OPC and QS. The investigation included assessments of changes in rheological properties, strength metrics, long-term shrinkage, resistance to sulfate attacks, freeze-thaw durability, microstructure analysis, and a cost-benefit evaluation. Test results indicated that biochar-incorporated samples exhibited up to a 20% increase in heat evolution by the end of the seventh day and plastic energy at 28 days that rose to 32.14% as compared to control samples in 20% biochar-augmented versions. Shrinkage reduction varied between 58 and 69% at 210 days for samples with 20% biochar. Specifically, the mix containing 20% biochar (G2-M5-BC-20) significantly improved the 90-day compressive and flexural strength by 8.9 and 9.3%, and 30.6 and 36.8%, respectively, while further inclusion of biochar showed no marked enhancement in performance metrics. The G2-M5-BC-20 mix also demonstrated excellent resistance to sulfate attacks and freeze-thaw cycles, exhibiting the least mass loss and highest residual compressive strength. An initial cost-benefit revealed that biochar-enhanced UHPC could offer compelling financial benefits. Given its mechanical behavior, potential for harmful CO2 emissions, and economic viability, the G2-M5-BC-20 mix emerged as the most promising formulation, potentially generating an overall profit of $36 per cubic meter.

Experimental investigation on the low‐velocity impact response and the residual strength of CFRP tubes

AbstractWith the help of the high‐speed camera and self‐designed fixture, it was investigated that the effects of the impactors in a variety of shapes on the mechanical behavior and failure mode of carbon fiber‐reinforced polymer (CFRP) tubes with a range of inner diameter during the low‐velocity impact (LVI) of four impact energies. Then, the three‐dimensional digital image correlation (3D‐DIC) system was carried out to monitor the damage evolution of the LVI‐damaged specimens under compressive and flexural loading. In addition, the residual compressive and flexural strength of all kinds of cases were compared and discussed. The results show that the increase in wall thickness can improve the LVI, compression‐after‐impact (CAI), and flexure‐after‐impact performance. The failure mode of compression changes to brittle fracture failure at the impact circumferential region. The CAI strength of the specimen damaged by a flat impactor is 23.89% less than that of a hemispherical one, but there is little difference in flexural loading.Highlights Mechanical behavior on in & post LVI of CFRP tubes varying wall thickness and impactor. Due to point‐line contact for flat impactor, two peak forces are in the F‐D curves. LVI property and residual strength are improved with the increase of wall thickness. Compressive failure mode is brittle fracture at the impact circumferential area. Flexure‐after‐impact strength mainly depends on the no‐impact surface of tubes.

Performance of reactive powder concrete with different fibres after high-temperature exposure

Reactive powder concrete (RPC) is used in structures such as radioactive storage plants, tall buildings and power plants. The performance of RPC after high-temperature exposure is therefore important. RPC (110 MPa) was prepared with different fibres (polypropylene fibres (PPF), polyester fibres (PEF) and their combination) at an optimum fibre dosage of 0.5% by weight of cement. The fibre-reinforced RPCs were exposed to temperatures of 200–800°C for different durations (30–120 min). Physical characteristics like colour change, fracture formation, weight loss, water absorption and residual compressive strength were evaluated. Ultrasonic pulse velocity tests were conducted. Scanning electron microscopy was used to observe the microstructure and assess the deterioration of hydrated substances after exposure to extreme temperatures for different durations. An increase in compressive strength was found for all fibre-reinforced RPCs after heating to 200°C for up to 120 min. The strength increased for 30-min exposure to 400°C. The strength of the fibre-reinforced RPCs decreased for all durations of 600°C and 800°C exposure. At these temperatures, the PEF-reinforced RPC had 10–15% greater residual strength than the RPCs. The PPF-reinforced RPC absorbed 6–12% more water than the RPCs made with PEF fibres after 120 min exposure to 800°C.

Research of the New Laboratory Methodology for Measuring the Disintegration of Mixtures with Inorganic Binders Hardened by Dehydration

The paper deals with the possibilities of using alkali silicate based inorganic binders for automotive industry aluminium castings production. In recent years, inorganic binders are coming back to the foreground and their manufacturers are developing new processes, which are starting to progressively supersede organic binder systems. Paper describes known knowledge about classic alkali silicate binders with focus on hardening processes and on improving their technological properties. Trends from the area of development and the use new alkali silicate based inorganic binders are also shortly described. As part of the experimental work, specific methods of producing samples were developed, with the help of which properties such as disintegration were subsequently evaluated by measuring abrasion and residual strengths. Characteristics such as residual compressive strength or shear strength at different thermal loads were also evaluated. When comparing the laboratory results with the results of de-coring in real conditions, a high degree of correlation was achieved, which makes it possible to determine the optimal recipe/procedure for the production of geometrically complex cores.