Mechanical characterization of lightweight engineered geopolymer composites exposed to elevated temperatures

In this study, the effect of different factors, such as PVA fibers (2% by total volume) and precursor type (slag, fly ash, or a combination of both), on the behavior of green lightweight engineered geopolymer composites (LEGC) and lightweight engineered cementitious composites (LECC) after exposure to temperatures up to 800 °C for 1 h is investigated. Expanded glass granules were used as lightweight aggregate instead of silica sand to reduce the spalling tendency and density of the composite. The flowability, density, color change, mass loss, spalling resistance, residual mechanical properties (compressive strength, stress-strain diagram, tensile stress-strain diagram, load-deflection response, failure mode), and microstructural analysis (by scanning electron microscopy) were investigated before and after exposure to thermal deterioration. The findings pointed out that the dry density, compressive strength, fiber bridging stress, strain capacity, maximum load, and maximum deflection of the developed mixtures before exposure to fire deterioration were in the range of 1703–1883 kg/m³, 16.66–64.11 MPa, 2.66–4.97 MPa, 2.40–3.33%, 1573–4824 N, and 2.92–5.53 mm respectively. It's worth mentioning that the substitution of 50% slag in the lightweight EGC mixture demonstrated the optimal tensile strain capacity and deformation capacity and further enhanced both ultimate tensile strength and flexural strength of fly ash-based EGC (FA-EGC) mixtures. After heat exposure, both LEGC and LECC composites demonstrated strain hardening behavior and deflection hardening behavior up to 300 °C of heat treatment, while after exposure to a temperature of 300 °C and above, both deflection hardening behavior and strain hardening behavior are dramatically damaged. This is attributable to the melting of the PVA fibers. Also, the microstructural analysis showed that incorporating fly ash into lightweight EGC mixtures can effectively reduce the melting point of PVA fibers and further improve the fire resistance of EGC mixtures.     

Dynamic mechanical properties of carbon fiber reinforced geopolymer concrete at different ages

In order to improve the strength and toughness of geopolymer concrete (GC) at different ages under impact load, using slag and fly ash as cementitious materials, NaOH and sodium silicate as alkaline activators, carbon fiber as reinforcement, carbon fiber reinforced geopolymer concrete (CFRGC) was prepared. The dynamic compression test of CFRGC was carried out by Φ 100 mm SHPB test system. The effects of age (3 d, 7 d, 28 d) and fiber content on the dynamic mechanical properties of CFRGC were studied, and the strengthening and toughening effects of carbon fiber on GC were analyzed. In addition, the strengthening and toughening effects of carbon fiber on GC and ordinary Portland cement based concrete (PC) were compared and analyzed. The results show that the performance indicators of CFRGC at different ages have strain rate effect under impact load, and the dynamic compressive strength and specific energy absorption of CFRGC increase approximately linearly with the strain rate. With the increase of age, the dynamic compressive strength and specific energy absorption of CFRGC increase, and the strain rate sensitivity of dynamic compressive strength and specific energy absorption also increases. With the increase of carbon fiber content, the dynamic compressive strength and specific energy absorption of CFRGC increase first and then decrease, and the strain rate sensitivity of dynamic compressive strength and specific energy absorption also increase first and then decrease. When the carbon fiber content is 0.2%, the dynamic mechanical properties of CFRGC are the best, and the strain rate sensitivity of performance indicators is the strongest. Carbon fiber has strengthening and toughening effects on GC and PC. When the fiber content is 0.2%, carbon fiber has the best strengthening and toughening effects on GC and PC. The strengthening and toughening effects of carbon fiber on GC is better than that of PC. Compared with 28 d, carbon fiber has better strengthening and toughening effects on GC at the ages of 3 d and 7 d.     

Effects of elevated temperature on pumice based geopolymer composites

Abstract

Aluminosilicate type materials can be activated in alkaline environment and can produce geopolymer cements with low environmental impacts. Geopolymers are believed to provide good fire resistance so the effects of elevated temperatures on mechanical and microstructural properties of pumice based geopolymer were investigated in this study. Pumice based geopolymer was exposed to elevated temperatures of 100, 200, 300, 400, 500, 600, 700 and 800°C for 3?h. The residual strength of these specimens were determined after cooling at room temperature as well as ultrasonic pulse velocity, and the density of pumice based geopolymer pastes before and after exposing to high temperature was determined. Microstructures of these samples were investigated by Fourier transform infrared for all temperatures and SEM analyses for samples that were exposed to 200, 400, 600 and 800°C. Specimens, which were initially grey, turned whitish accompanied by the appearance of cracks as temperatures increased to 600 and 800°C. Consequently, compressive strength losses in geopolymer paste were increased with increasing temperature level. On the other hand, compressive strength of geopolymer paste was less affected by high temperature in comparison with the ordinary Portland cement. As a result of this study, it is concluded that pumice based geopolymer is useful in compressive strength losses exposed to elevated temperatures.     

Mechanical and chemical properties of metakaolin-based geopolymer exposed to elevated temperature

A method is presented to fabricate metakaolin-based geopolymers that are structurally and mechanically stable up to 600°C. The chemical environment of the geopolymers is characterized using thermogravimetric analysis and Fourier-transform infrared spectroscopy. Residual free water turned into steam and caused damage to the geopolymer when exposed to elevated temperatures. The curing temperature was increased from 80 to 120°C to remove water during the curing process. A correlation was drawn between the amount of Si-O-Al linkage formed and the position of fingerprint peaks in infrared spectra, providing a tool to evaluate the level of geopolymerization. Flexural and tensile properties of geopolymers fabricated using the optimized method were measured for no heat treatment and for exposure to elevated temperatures of 200, 400, and 600°C. The flexural strength was measured to be 10.80 ± 2.99 MPa at room temperature, 10.36 ± 0.64 MPa at 400°C, and 8.04 ± 1.60 MPa at 600°C. The flexural modulus is reported to be 13.09 ± 3.40 GPa at room temperature and 11.03 ± 0.53 GPa at 600°C. The flexural toughness decreased with increasing temperature. The tensile properties of the geopolymer were measured with direct tensile tests paired with an extensometer. The tensile strength decreased from 4.16 ± 2.08 MPa at room temperature to 3.13 ± 0.97 MPa at 400°C, and 2.75 ± 0.86 MPa at 600°C. The Young's modulus decreased from 45.38 ± 30.30 GPa at room temperature to 26.88 ± 6.65 GPa at 600°C. Both flexural and tensile tests have shown that the metakaolin-based geopolymers cured at 120°C is mechanically stable at temperatures up to 600°C.     

Effect of elevated temperatures on geopolymer paste, mortar and concrete

Geopolymers are generally believed to provide good fire resistance due to their ceramic-like properties. Previous experimental studies on geopolymer under elevated temperatures have mainly focused on metakaolin-based geopolymers. This paper presents the results of a study on the effect of elevated temperature on geopolymer paste, mortar and concrete made using fly ash as a precursor. The geopolymer was synthesized with sodium silicate and potassium hydroxide solutions. Various experimental parameters have been examined such as specimen sizing, aggregate sizing, aggregate type and superplasticizer type. The study identifies specimen size and aggregate size as the two main factors that govern geopolymer behavior at elevated temperatures (800 °C). Aggregate sizes larger than 10 mm resulted in good strength performances in both ambient and elevated temperatures. Strength loss in geopolymer concrete at elevated temperatures is attributed to the thermal mismatch between the geopolymer matrix and the aggregates.     

Numerical modeling of transport phenomena in reinforced concrete exposed to elevated temperatures

The objective of this study is to develop a finite difference model that simulates coupled heat and mass transport phenomena in reinforced concrete structures exposed to rapid heating conditions such as fires. A mathematical and computational model for simulating the multidimensional, thermohydrological response of reinforced concrete structural elements is developed and subsequently used to study the effects of steel reinforcement on thermodynamic state variables. Key material parameters describing multiphase fluid flow and thermohydrological behavior of concrete are discussed. Spatial and temporal distributions of temperature, pore pressure, and degree of saturation are illustrated as predicted under extreme thermal-loading conditions. Simulation results indicate that the presence of steel reinforcement impedes moisture movement and produces quasi-saturated zones in cover concrete where significant pore pressures are developed.     

Dynamic compressive behavior of basalt fiber reinforced concrete after exposure to elevated temperatures

This paper investigated the dynamic behavior of basalt fiber reinforced concrete (BFRC) after elevated temperatures by using a 100‐mm‐diameter split Hopkinson pressure bar apparatus. Changes in weight and ultrasonic pulse velocity (UPV) were also studied. The results indicate that the weight losses of BFRC before cooling increase with temperature, while a reduction in weight loss value is observed after water cooling. The UPV values of BFRC decrease constantly as temperature increases, and the measured velocities under the same temperature increase with fiber content as temperature exceeds 200 °C. For a given temperature, the strain rate, dynamic strength, critical strain, and impact toughness of BFRC increase with impact velocity. For a given impact velocity, the increasing temperature generally leads to an increase in strain rate and critical strain and results in a decrease in dynamic strength and impact toughness except in the case of 200 °C. At 200 °C, however, a marginal reduction, even an improvement in dynamic strength is observed, and the impact toughness initially decreases, then increases with loading rate when compared with that at room temperature. Basalt fiber is effective in improving the strength performance, deformation capacity, and energy absorption property of concrete after high temperature. Copyright © 2015 John Wiley & Sons, Ltd.     

Development of lightweight aggregate geopolymer concrete with shale ceramsite

This paper developed a lightweight aggregate geopolymer concrete (LAGC) with shale ceramsite. 18 groups of LAGC specimens with 3 sand ratios (30%, 40% and 50%) and 6 aggregate contents (10%, 20%, 30%, 40%, 50% and 60%) were prepared. A series of static tests (dry density test and uniaxial compression test) and dynamic tests (ultrasonic pulse velocity test) were performed to achieve the dry density, compression strength and P-wave velocity. The effects of sand ratio and aggregate content on the dry density, compression strength and P-wave velocity were discussed. Two optimal mix proportions for the LAGC were proposed. The results show that the dry density and P-wave velocity increase as sand ratio increases. The compressive strength increases then decreases as sand ratio increases. In addition, the dry density and compressive strength decrease as aggregate content increases. The P-wave velocity increases as aggregate content increases. The LAGC with the sand ratio of 30% and aggregate contents of 30% reaches the dry density of 1378.0 kg/m³ and compressive strength of 18.5 MPa. The LAGC with the sand ratio of 30% and aggregate contents of 40% reaches the dry density of 1348.0 kg/m³ and compressive strength of 16.8 MPa. Both of the proportions satisfied the engineering requirements, which are recommended for the potential application in the construction.     

Thermal and mechanical properties of light‐weight concrete exposed to high temperature

The extensive studies devoted so far to normal‐strength light‐weight aggregate concrete (LWAC or LWC) have exhaustively clarified its behaviour in ordinary conditions. However, the introduction of high‐performance light‐weight aggregate concrete (HPLWAC or HPLWC), containing such pozzolanic components as microsilica and fly ash, raises some concerns, for instance about the behaviour at high temperature and after cooling. To investigate the temperature‐induced mechanical damage, both in compression and tension, of silica‐fume HPLWCs, a systematic research program was carried out at the Politecnico di Milano on materials residual behaviour (testing after cooling down to room temperature). Three concrete mixes (Normal‐Strength Concrete = NSC, f_c²⁰ = 30 MPa; Light‐Weight Concrete = LWC, f_c²⁰ ≈ 40 MPa; and High‐Performance Light‐Weight Concrete = HPLWC, f_c²⁰ ≈ 60 MPa), five temperature levels (20, 105, 250, 500 and 750 °C, no loads applied during heating), one thermal state (after cooling), three nominally‐equal tests for each case (for repeatability) were planned, bringing the total number of specimens to 120 (45 tested in compression, 45 in direct tension and 30 in indirect tension by splitting). At the same time, the thermal diffusivity of the materials was evaluated up to 750 °C (4 specimens). The results show that HPLWC is somewhat more temperature‐sensitive than both NSC and LWC, but this extra sensitivity is counterbalanced by HPLWC's lower diffusivity. Its better insulation properties are advantageous for the concrete in axially‐loaded members and for the tension bars in the beams, as demonstrated by the thermo‐mechanical analyses of three typical R/C sections (rectangular, T and slab sections) carried out in the second part of the paper. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanical and acoustic absorption properties of lightweight fly ash/slag-based geopolymer concrete with various aggregates

Acoustic absorption and thermal insulation play a key role in modern buildings to make living comfortable and energy-saving. This paper aims to study the workability, physical and mechanical properties, thermal conductivity, and acoustic absorption of modified geopolymer concrete (GPC) with various types of lightweight aggregates (LWA) such as extruded polystyrene foam beads waste (EPS), vermiculite, or lightweight expanded clay aggregate (LECA). The mixtures of geopolymer concrete have been modified by substituting for the ordinary aggregates (dolomite) by volume with various ratios of 0, 25, 50, 75, and 100% for each type of LWA. Besides, the mechanisms of specimens were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and mapping. The results illustrated that the compressive strength values range between 8.5 and 47.50 MPa. The hardened density of concrete was between 1500 and 2450 kg/m³, and thermal conductivity was between 0.45 and 1.16 W/m.K. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. EPS, vermiculite, and LECA will be beneficial for applications in lightweight geopolymer concrete due to their capability to reduce weight and excellent thermal conductivity, and the property of improving acoustic absorption. The mechanical results indicated that 25% LECA was the best compared with the ratios of other LWA and gained 35.0, 2.7, and 4.3 MPa of compressive, splitting tensile and flexural strength, respectively. It had positive workability; the thermal conductivity was 1.1 W/m.K, and hardened density was decreased to 10% compared to the control. In addition, LECA is considered the superior and suitable material for acoustic absorption compared with other aggregates.     

Effect of polypropylene fibers on thermogravimetric properties of self‐compacting concrete at elevated temperatures

In this study, the effect of polypropylene (PP) fibers on thermogravimetric parameters of self‐compacting concrete (SCC) containing indigenous materials was investigated experimentally and statistically. The mixes containing cement, water, fly ash, fine aggregate, coarse aggregate, and super plasticizer, with the addition of PP fibers (0%, 0.05%, 0.1%, and 0.15%) by volume of the mixtures, were prepared. The physical properties of SCC were determined at elevated temperatures (200, 400, and 600 °C) after cooling in the laboratory. Regression models were developed to determine the responses, and the optimum amount of 0.05% PP fibers by volume was measured. Copyright © 2012 John Wiley & Sons, Ltd.     

Compressive behavior of fiber reinforced high-performance concrete subjected to elevated temperatures

In this paper, the effects of elevated temperatures on the compressive strength stress–strain relationship (stiffness) and energy absorption capacities (toughness) of concretes are presented. High-performance concretes (HPCs) were prepared in three series, with different cementitious material constitutions using plain ordinary Portland cement (PC), with and without metakaolin (MK) and silica fume (SF) separate replacements. Each series comprised a concrete mix, prepared without any fibers, and concrete mixes reinforced with either or both steel fibers and polypropylene (PP) fibers. The results showed that after exposure to 600 and 800 °C, the concrete mixes retained, respectively, 45% and 23% of their compressive strength, on average. The results also show that after the concrete was exposed to the elevated temperatures, the loss of stiffness was much quicker than the loss in compressive strength, but the loss of energy absorption capacity was relatively slower. A 20% replacement of the cement by MK resulted in a higher compressive strength but a lower specific toughness, as compared with the concrete prepared with 10% replacement of cement by SF. The MK concrete also showed quicker losses in the compressive strength, elastic modulus and energy absorption capacity after exposure to the elevated temperatures. Steel fibers approximately doubled the energy absorption capacity of the unheated concrete. They were effective in minimizing the degradation of compressive strength for the concrete after exposure to the elevated temperatures. The steel-fiber-reinforced concretes also showed the highest energy absorption capacity after the high-temperature exposure, although they suffered a quick loss of this capacity. In comparison, using PP fibers reduced the energy absorption capacity of the concrete after exposure to 800 °C, although it had a minor beneficial effect on the energy absorption capacity of the concrete before heating.     

Experimental research on the dynamic compressive properties of lightweight slag based geopolymer

The present study aims at preparing lightweight slag based geopolymer (LW-SG) and studying its mechanical properties under dynamic and quasi-static loads. Firstly, three LW-SG with different densities were prepared by replacing the slag with expanded perlite (EP). Secondly, the density, wave velocity and pore structure of LW-SG with different EP contents were tested. Thirdly, the mechanical properties under quasi-static and dynamic loads were compared. Finally, the effects of the strain rate and EP content on the mechanical properties and failure modes of LW-SG were discussed. The results showed that with the EP contents increase, the dry density and longitudinal wave velocity gradually decreased, while the porosity increased. In addition, the quasi-static compressive strength and elastic modulus of LW-SG increased with curing ages, but decreased with EP contents increased. The dynamic compressive strength, dynamic increase factor, strain energy density and damaged degree of LW-SG all showed an increasing tendency with the strain rates increase, which exhibits an obvious strain rate dependence. Under the same strain rate, the dynamic compressive strength and strain energy density decreased with the EP contents increase, while the damaged degree increased with the EP contents increase.     

Effect of elevated temperatures on mechanical properties of high‐strength concrete containing varying proportions of hematite

Aggregates typically constitute 70 to 80 wt% of concrete, and therefore their type, size, and structure play an essential role in modifying the properties of concrete. When concrete is used for shielding nuclear applications, temperature is also a key factor. This study investigates the effects of elevated temperatures (25 °C, 200 °C, 400 °C, 600 °C, and 800 °C), heating durations (1, 2, and 3 h), and cooling regimes (air, and water cooling) on mechanical properties of concrete containing different proportions of hematite. A sample of plain concrete was produced for comparison purposes by using river sand, crushed sand, and crushed aggregates. Replacement ratios of 15%, 30%, 45%, and 60% were used for hematite aggregates. The cement content and water–cement ratio were 450 kg/m³ and 0.38, respectively. Slump values of fresh concretes as well as unit weight, compressive strength, flexural strength, splitting tensile strength, and elasticity modulus values of hardened concrete were determined. The addition of hematite into concrete seems to improve its mechanical properties, and hematite concretes have better thermal stability at elevated temperatures than plain concrete does. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessment of recycling use of GFRP powder as replacement of fly ash in geopolymer paste and concrete at ambient and high temperatures

Environmental issues caused by glass fiber reinforced polymer (GFRP) waste have attracted much attention. The development of cost-effective recycling and reuse methods for GFRP composite wastes is therefore essential. In this study, the formulation of the GFRP waste powder replacement was set at 20–40 wt%. The geopolymer was formed by mixing GFRP powder, fly ash (FA), steel slag (SS) and ordinary Portland cement (OPC) with a sodium-based alkali activator. The effects of GFRP powder content, activator concentration, liquid to solid (L/S) ratio, and activator solution modulus on the physico-mechanical properties of geopolymer mixtures were identified. Based on the 28-day compressive strength, the optimal combination of the geopolymer mixture was determined to be 30 wt% GFRP powder content, an activator concentration of 85%, L/S of 0.65, and an activator solution modulus of 1.3. The ratios of compressive strength to flexural strength of the GFRP powder/FA-based geopolymers were considerably lower than those of the FA/steel slag-based geopolymers, which indicates that the incorporation of GFRP powder improved the geopolymer brittleness. The incorporation of 30% GFRP powder in geopolymer concrete to replace FA can enhance the compressive and flexural strengths of geopolymer concrete by 28%. After exposure to 600 °C, the flexural strength loss for geopolymer concretes containing 30 wt% GFRP powder was less than that of specimens without GFRP powder. After exposure to 900 °C, the compressive strength and flexural strength losses of geopolymer concretes containing 30 wt% GFRP powder were similar to those of specimens without GFRP powder. The developed GFRP powder/FA-based geopolymers exhibited comparable or superior physico-mechanical properties to those of the FA-based geopolymers, and thus offer a high application potential as building construction material.     

Mechanical properties and microstructure of high strength concrete containing polypropylene fibres exposed to temperatures up to 200 °C

High strength concrete has been used in situations where it may be exposed to elevated temperatures. Numerous authors have shown the significant contribution of polypropylene fibre to the spalling resistance of high strength concrete. This investigation develops some important data on the mechanical properties and microstructure of high strength concrete incorporating polypropylene fibre exposed to elevated temperature up to 200 °C. When polypropylene fibre high strength concrete is heated up to 170 °C, fibres readily melt and volatilise, creating additional porosity and small channels in the concrete. DSC and TG analysis showed the temperature ranges of the decomposition reactions in the high strength concrete. SEM analysis showed supplementary pores and small channels created in the concrete due to fibre melting. Mechanical tests showed small changes in compressive strength, modulus of elasticity and splitting tensile strength that could be due to polypropylene fibre melting.     

Compressive strength of fly‐ash‐based geopolymer concrete at elevated temperatures

This paper presents the compressive strength of fly‐ash‐based geopolymer concretes at elevated temperatures of 200, 400, 600 and 800 °C. The source material used in the geopolymer concrete in this study is low‐calcium fly ash according to ASTM C618 class F classification and is activated by sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH) solutions. The effects of molarities of NaOH, coarse aggregate sizes, duration of steam curing and extra added water on the compressive strength of geopolymer concrete at elevated temperatures are also presented. The results show that the fly‐ash‐based geopolymer concretes exhibited steady loss of its original compressive strength at all elevated temperatures up to 400 °C regardless of molarities and coarse aggregate sizes. At 600 °C, all geopolymer concretes exhibited increase of compressive strength relative to 400 °C. However, it is lower than that measured at ambient temperature. Similar behaviour is also observed at 800 °C, where the compressive strength of all geopolymer concretes are lower than that at ambient temperature, with only exception of geopolymer concrete containing 10 m NaOH. The compressive strength in the latter increased at 600 and 800 °C. The geopolymer concretes containing higher molarity of NaOH solution (e.g. 13 and 16 m ) exhibit greater loss of compressive strength at 800 °C than that of 10 m NaOH. The geopolymer concrete containing smaller size coarse aggregate retains most of the original compressive strength of geopolymer concrete at elevated temperatures. The addition of extra water adversely affects the compressive strength of geopolymer concretes at all elevated temperatures. However, the extended steam curing improves the compressive strength at elevated temperatures. The Eurocode EN1994:2005 to predict the compressive strength of fly‐ash‐based geopolymer concretes at elevated temperatures agrees well with the measured values up to 400 °C. Copyright © 2014 John Wiley & Sons, Ltd.     

Residual compressive behavior of alkali‐activated concrete exposed to elevated temperatures

This paper reports the effect of elevated temperature exposures, up to 1200^°C , on the residual compressive strengths of alkali‐activated slag concrete (AASC) activated by sodium silicate and hydrated lime; such temperatures can occur in a fire. The strength performance of AASC in the temperature range of 400–800^°C was similar to ordinary Portland cement concrete and blended slag cement concrete, despite the finding that the AASC did not contain Ca(OH)₂ , which contributes to the strength deterioration at elevated temperatures for Ordinary Portland Cement and blended slag cement concretes. Dilatometry studies showed that the alkali‐activated slag (AAS) paste had significantly higher thermal shrinkage than the other pastes while the basalt aggregate gradually expanded. This led to a higher thermal incompatibility between the AAS paste and aggregate compared with the other concretes. This is likely to be the governing factor behind the strength loss of AASC at elevated temperatures. Copyright © 2008 John Wiley & Sons, Ltd.     

Mechanical and microstructural evolutions of fly ash/slag-based geopolymer at high temperatures: Effect of curing conditions

Designing a building material with excellent heat resistance is crucial for protection against catastrophic fires. Geopolymer materials have been investigated as they offer better heat resistance than traditional cement owing to their ceramic-like properties. Curing temperature and conditions are crucial factors that determine the properties of geopolymers, but their impacts on the heat resistance of geopolymers remain unclear. This study produced geopolymers from fly ash and ground granulated blast furnace slag by using sodium silicate and sodium hydroxide solutions as alkaline solutions. To examine the effect of curing conditions on the high-temperature performance of geopolymer, four different curing conditions, namely, heat curing (70 °C for 24 h), ambient curing (20 °C), water curing, and the combination of heat and water curing (70 °C for 24 h followed by water curing), were applied. At 28 d, the specimens were subjected to high temperatures (500 °C, 750 °C, and 950 °C), and their mechanical and microstructural evolutions were studied. The results revealed that the curing condition significantly affects the properties of the unexposed geopolymer; the effect on its high-temperature performance is insignificant. Furthermore, all the specimens could maintain adequate compressive strength after exposure to the maximum temperature of 950 °C, promising the use of geopolymer for structural applications.     

动力载荷作用下橡胶混凝土的力学性能

采用体积分数分别为15%、30%和45%的橡胶粉或橡胶块颗粒对混凝土中粗骨料进行替换,并用自由振动法对橡胶混凝土简支梁的振动频率和阻尼性能进行测试,考察了小变形时阻尼比与橡胶颗粒大小和数量之间的关系。采用弹性波法和梁单元法对橡胶混凝土的动力模量进行了测量,并对其静弹性模量与动弹性模量进行了对比。结果表明,橡胶混凝土的动力弹性模量低于普通混凝土。橡胶块对橡胶混凝土动、静弹性模量的影响均大于橡胶粉。普通混凝土的动弹性模量比静弹性模量高37.4%,而橡胶混凝土的动弹性模量比静弹性模量高约50%。橡胶混凝土的阻尼比随最大响应幅值的增大而增大。相比于普通混凝土,橡胶混凝土的阻尼对振动的响应更为敏感。橡胶混凝土的阻尼比随橡胶含量的增加而显著增大。当橡胶的体积分数为30%时,橡胶混凝土综合性能较佳。