Compressive Strength Of Pastes Research Articles

Influence of raw material properties on microscopic and mechanical characteristics of alkali-activated materials

Alkali-activated fly ash and slag pastes are considered a new low-carbon cementitious material with good mechanical characteristics and durability. However, the mechanical characteristics of the alkali-activated materials are uncertain due to the multiplicity of the raw material properties. Few studies clarify how the raw material properties affect the mechanical characteristics of hardened pastes. The correlation between the raw material properties and the reaction rate, product composition, gel content, and pore size distribution is discussed in this study. The increase in the CaO content of the precursor will accelerate the degree of alkali activation. In this case, the reaction production becomes relatively more, and the pore size distribution becomes relatively denser, improving the compressive strength of the pastes. Moreover, the effects of the activator modulus and alkali content on the compressive strength of the pastes are not monotonically increasing. The excessive alkali will cause the surface of raw material particles to form a gel layer quickly, which could prevent the further alkali activation of the particles. This case is not conducive to gel formation and will cause the pore structure of the hardening pastes to be relatively loose. Furthermore, the influence of activator modulus on the compressive strength of pastes is lower than that of alkali content. Excess activator modulus is also unfavourable for pore structure densification.

Mechanical properties and microstructure evolution of phosphate slag-cement based materials under varied curing temperatures

Recycling of wasted phosphate slag (PS) into useful mineral additives shows great significance not only in carbon reduction but also contributes to the availability of green additives to cement-based materials. This work aims to explore a feasible way of disclose the mechanism of PS added cement-based materials. It was found that compressive strengths of pastes were all declined with increasing addition of PS both at early age of 2 d and long age of 28 d, increased the curing temperatures from 20 °C to 40 °C helped to improve the above situation. A remarkable increase of compressive strength in 10SF+20PS sample with the value of 55.48 MPa was obtained at 28 d. The enhanced mechanical property was related with the generation of large amount of hydration products such as C–S–H, Ca(OH)2 and AFt.

Evaluation of calcium carbide residue and fly ash as sustainable binders for environmentally friendly loess soil stabilization

The incorporation of waste materials into cementitious binders serves as a strategy to diminish waste volume and lower carbon emissions. This study presents an in-depth evaluation of calcium carbide residue and coal fly ash as alternative binders. The assessment of raw materials emphasized their chemical composition and potential for pozzolanic reactions. Based on these factors, the optimal ratio of Ca/(SiO2 + Al2O3) in the raw materials was determined to be 1.5. Therefore, this study was designed to vary the raw material composition with a CaO/(SiO2 + Al2O3) ratio ranging from 1.7 to 0.9. Upon investigating the effect of the raw material proportion on the compressive strength of pastes and mortars, the composition yielding the highest compressive strength was selected for its potential application as a stabilizer for loess soil. A mixture of calcium carbide residue and coal fly ash with a Ca/(SiO2 + Al2O3) ratio of 1.5 resulted in the highest compressive strength at long curing periods in both pastes and mortars. Mineralogical and microstructural analyses revealed several products, beyond those formed from the pozzolanic reactions, that occurred and enhanced the compressive strength of samples. The highest performing mixture of carbide residue and coal fly ash was then used to stabilize loess soil at 10–25 wt%. The unconfined compressive strength, along with mass and strength loss due to wetting and drying cycles, was also studied. It was observed that the unconfined compressive strength of the stabilized soils remained consistent after six wet-dry cycles but decreased after twelve cycles due to microcracks. The findings suggest that carefully designed mixtures based on the chemical interactions of calcium carbide residue and coal fly ash can offer a sustainable, efficient approach for soil stabilization, potentially revolutionizing construction practices.

Hydration properties of composite cementitious materials containing steel slag under steam curing condition

Steel slag (SS) is a by-product of the steel industry, and its recycling is of great significance. In this study, the influence of SS fineness and curing regimes on the hydration properties of cement and the effects of SS content on the compressive strength of pastes were investigated. The hydration products and microstructure of pastes were further explored through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the compressive strength decreases gradually with the increase of SS, and increases with the increase of the specific surface area of SS. The compressive strength of paste after steam curing is improved, and the compressive strength of the paste mixed with 30% SS can reach more than 50 MPa after 90 days of steam curing. The hydration products of paste mixed with SS are not significantly different from those of cement, which mainly comprise calcium hydroxide (Ca(OH)2) and calcium silicate hydrate (C–S–H) gel, accompanied by a small amount of calcium carbonate (CaCO3). SS has secondary hydration after long-term ageing and can fill and refine the pore structure, according to SEM. Using SS as a supplementary material is beneficial in terms of reducing cement cost and lowering carbon dioxide (CO2) emission.

Synergistic effect of aluminum sulfate and triethanolamine on the hydration of metakaolin blended cement

AbstractShotcrete is regarded as an indispensable component in the construction of tunnels and mines, which can stabilize the tunnel wall and prevent groundwater infiltration. Along with the massive railway construction in China's mountainous region, it is unavoidable to build more tunnels, and then the used amount of shotcrete increases dramatically. Calcined clay blended cement is one promising low‐carbon cementitious material and metakaolin (MK) is the main reactive component in calcined clay. Considering the high demand for shotcrete and the urgently needed carbon neutrality in China, it is necessary to contain more MK in the cement of shotcrete.Beside the cement, accelerator is also necessary for the production of shotcrete. Aluminum sulfate (AS) and triethanolamine (TEA) are two representative components in the alkali‐free liquid accelerator. However, limited researches were conducted regarding the synergistic effect of AS and TEA on the setting and hardening performance of the metakaolin blended cement (OPC‐MK).Hence, in order to clarify the effect of TEA and AS on the hydration of OPC‐MK, different dosages of TEA were added to AS solution and their effects on setting performance, compressive strength and hydration kinetics of OPC‐MK were investigated. It is found that, with the presence of both AS and TEA, a high dosage of TEA facilitates the reaction of the aluminate phase while greatly retards the silicate reaction. More importantly, TEA can promote the dissolution and pozzolanic reaction of MK. Thereby a dense structure can be formed and the compressive strength of pastes at 28 d is enhanced. At last, the interactions between TEA, AS and OPC‐MK is thoroughly analyzed, which could provide a theoretical basis for the wide application of low‐carbon cement in shotcrete.

Forecasting the strength of micro/nano silica in cementitious matrix by machine learning approaches

This work provides an intelligent machine learning-based technique for anticipating cement paste compressive strength incorporating nanocomposite. In this approach, artificial neural network (ANN), gene expression programming (GEP), random forest (RF), and ensemble approaches are used to combine multiple weak learners capable of identifying the mapping between input and output data into a robust learner. The accuracy of the strong learner as a whole will be increased by incorporating the weak learner with the least prediction error with enhanced correlation. The components of the cement paste mixture (such as water-to-cement ratio, nano-silica (%), micro-silica (%), curing time (days), and the compressive strength value are used as input data and output data. Thus, 205 datasets of cement compressive strength tests are collected to train and assess the learners. The reliability of the models was evaluated using cross-validation with K-folding and statistical error analysis (i.e., MAE, MAE, and RMSE). Therefore, interpretable methods using AdaBoost provide a significant correlation with a lower error rate of R2 = 0.96. The two that perform the best are ANN with ensemble Adaboost and RF with an R-square of 0.97. Additionally, the cross-validation findings demonstrate that the answer was correct and had minimal mistakes. The ensemble model, therefore, displays a strong connection. In addition, new expressions for the predictions of the 28-day compressive strength of nanocomposite containing silica content are developed based on the database. Sensitivity analysis reveals that curing time and silica content has a major influence on prediction. In addition, a model capable of predicting the values of the desired outputs when the necessary input parameters are provided is trained to generate the graphical user interface (GUI). It simplifies the procedure and provides a useful instrument for employing the model's civil engineering abilities.

The effect of boron oxide on the microstructure and hydration of calcium sulfoaluminate phase

Boron-rich waste causes numerous environmental problems when discharged directly into the environment. Here, various quantities of boron oxide (B2O3) were added to calcium sulfoaluminate (C4A3$) during the sintering process to demonstrate a potential use of boron-rich waste. The microstructure and hydration performance of C4A3$ with various B2O3 contents were investigated with scanning electron microscopy, x-ray diffraction, isothermal conduction calorimetry, thermogravimetric studies and compressive strength tests. B2O3-doped C4A3$ had a larger grain size than the pure phase; and were surrounded by amorphous phases. The presence of B2O3 was shown to promote the phase transition process through which C4A3$ changes from the orthorhombic to the cubic structure; and the substitution of Al3+ for B3+ in AlO4 tetrahedra was surveyed by structural refinements. As the B2O3 content increased, the induction period of C4A3$ increased while the hydration rate decreased because of the amorphous phases around the C4A3$. However, the hydration degree of doped C4A3$ increased due to the slower reaction rate. Thus, when an appropriate amount of B2O3 was added to the C4A3$ during sintering, a significant improvement in the compressive strength of pastes was observed.

Effects of construction waste powder on micro–macro properties of green high-strength cement paste with low water-to-binder ratio

The replacement of cement with ground construction waste powder is considered a sustainable strategy for the production of high-strength cement-based materials. This study investigated the influences of construction waste powder types and replacements on the micro–macro characterizations of green high-strength cement paste with low water-to-binder (w/b) ratio. The results highlighted that paste with 0.2 w/b ratio contained abundant hydration products and un-hydrated cement, and construction waste powder exerted good nucleation sites and filling effects in paste. The mix of construction waste powder did not change the hydration product types but reduced calcium hydroxide content in paste. Mixing appropriate ground brick powder up to 50% declined paste drying shrinkage, but the paste drying shrinkage continuously increased as ground paste/mortar/concrete powder content increases. The maximum drying shrinkage of paste with 50% ground brick powder and 50% ground concrete powder was 3.3% lower and 32.4% higher than the plain paste. When ground brick powder content was below 50% or ground paste/mortar/concrete powder content was below 30%, construction waste powder blended paste had similar or better compressive strength than plain paste, but incorporating 70% construction waste powder reduced the paste compressive strength. When construction waste powder content was identical, ground brick powder blended paste had higher compressive strength than paste containing ground paste/mortar/concrete powder. Incorporating appropriate dosage of ground brick powder reduced the transport properties and total porosity of paste, whereas the transport properties and total porosity both increased with ground paste/mortar/concrete powder incorporation. Optimizing construction waste powder types and contents can prepare green paste owning high-strength and low transport properties.

The Influence of Temperatures on the Hydration of Cement Paste at the Early Age, and Behaviour of Cement Paste with the Addition of Triethanolamine (TEA) and Triisopropanolamine (TIPA)

This paper intends to examine the influence of temperatures on the early age of cement paste hydration, as well as the setting time and the compressive strength of cement paste with the addition of Triethanolamine (TEA) and Triisopropanolamine (TIPA); hence, the mechanisms of TEA, and TIPA at different curing temperatures were explored. The outcomes show that adding 0.05% and 0.1% TEA, and 0.05% and 0.1% TIPA retarded the setting time of cement pastes; however, this retardation depended on both the dosage and the curing temperature. At 23°C curing temperature, both TEA and TIPA could be used as a hardening accelerator at the dosage of 0.05% by cement weight. Adding 0.05% TEA into the cement paste strongly accelerated the hydration of C3A and increased the early compressive strength, which was more efficient than adding 0.05% and 0.1% TIPA, especially after 8 hours of curing. However, at 50°C curing temperature, as TIPA strongly accelerated the formation of AFt, AFm, CH, using TIPA was more effective than using TEA to enhance the cement paste's compressive strength. These results can offer theoretical direction for the application of cement-based materials adding TEA and TIPA under hot and standard curing temperatures.

Concrete made with high-strength artificial geopolymer aggregates: Mechanical properties and failure mechanisms

Artificial geopolymer aggregates (GPA) provide an effective solution to simultaneously reduce the over-excavation of natural rock and mitigate the waste landfills. In this study, GPA with a paste compressive strength over 140 MPa were produced and used as coarse aggregates in concrete with different water-to-binder ratios (w/b = 0.3, 0.4, and 0.5). The mechanical properties and failure mechanisms of so-formed geopolymer aggregate concrete (GAC) were comprehensively investigated and compared with those of natural aggregate concrete (NAC). Although GPA showed inferior strength than natural aggregates, both the compressive and splitting tensile strengths of GAC were 8.0 % and 5.5 % higher than those of NAC, respectively, when w/b = 0.3. For the failure modes of GAC, cracks penetrated through both GPA and matrix when w/b = 0.3, while more aggregate/matrix interfacial cracks were observed as w/b increased. In comparison, major cracks propagated along the aggregate/matrix interface in NAC. From microhardness tests, the comparatively weak interfacial transition zone (ITZ) was observed in NAC, rather than in GAC. The micro-level observations demonstrated the existence of dense microstructures in GPA/matrix interfacial regions, especially when w/b is low. The findings provided a fundamental understanding of the mechanical properties and failure mechanisms of GAC, which is helpful for the future applications of GPA.

Utilizing nano-SiO2 for modifying the microstructure, strength and transport properties of sustainable cementitious materials with waste concrete powder

Using waste concrete powder as an alternative binder in green cementitious materials contributes to reduce the number of construction and demolition waste, and developing an effective method to modify the performance of waste concrete powder blended cementitious materials is necessary. The influences of nano-SiO2 at 0–3% dosage on cementitious materials containing waste concrete powder as partial cement replacement (0–50%), under a ratio of 1:2 for both water-to-binder and binder-to-sand, were investigated in this study with the aspects of micro-structure and macro-performance. The results illustrated that mixing waste concrete powder negatively impacted the hydration reaction and micro-structure of cement paste; however, the mix of nano-SiO2 promoted the secondary hydration reaction and refined pore diameter of waste concrete powder mixed paste. Mixing nano-SiO2 raised the drying shrinkage but reduced the water loss of paste including waste concrete powder. The replacement of cement by waste concrete powder caused the reduction in compressive strength of paste. But at a fixed substitution level of waste concrete powder in paste, the compressive strength rose with the increment of nano-SiO2 content up to 3%. The transport properties rose as waste concrete powder was incorporated in mortar, but the mix of nano-SiO2 significantly reduced the transport properties of waste concrete powder incorporated mortar. Particularly, the effects of nano-SiO2 addition on the decrease in water absorption became more distinct as high content of waste concrete powder was blended. Optimizing the content of waste concrete powder and nano-SiO2 can obtain green cementitious materials owning good strength and low transport properties.

PROPERTIES OF CONCRETE UTILIZING SELF-CEMENTING HIGH-CALCIUM FLY ASH AS SOLE BINDER MATERIAL

Fly ash, a waste material derived from the coal burning in power plants, could be utilized in concrete mixtures as a filler or as a cement replacement material, either partially or fully. Some papers also report that high-calcium fly ash can be utilized as a cementitious material through the hydration process. However, there are just a few papers that studied the behavior of concrete that utilizes high-calcium fly ash as the sole binder material without any chemical activators. Furthermore, there are no reports about whether the effect of the different water-to-cementitious ratios of this concrete is the same as the ordinary Portland cement concrete. This paper presents an initial development on the use of fly ash as a sole binder material, i.e., 100% fly ash concrete without any chemical solution as an activator. This research utilizes the high calcium content in the fly ash to produce concrete with a commonly used method (just add the water without any alkali activator) and investigates how the water-to-cementitious ratio can influence the compressive strength of the paste and the concrete as well. The calcium content in the fly ash used in this study was in the range of 19–22 percent of the total weight of fly ash. Paste compressive strength of 66.78 MPa was obtained at 28 days with a very low water-to-cementitious ratio of 0.110.

Influence of ion chelator on pore structure, water transport and crack-healing properties of cement pastes incorporating high-volume fly ash and blast-furnace slag

This paper focuses on the influence of ion chelator (CA) on pore structure, water transport and self-healing ability of cement pastes incorporating high content fly ash (FA) and blast-furnace slag (BFS). The pore structure of pastes was measured by low-field nuclear magnetic resonance (LF-NMR). The water transport property was tested by water absorption test. The self-healing ability was assessed by water permeability and crack healing test. Results showed that the compressive strength of hardened pastes was promoted by CA, the increase rates in compressive strength of pastes were 21.9% (50%BFS), 15.7% (pure cement), 9.9% (30%FA) and 8.8% (16%FA24%BFS). CA decreased the proportion of small capillary pores (0.01–0.1 μm) in cement pastes which were more pronounced for the water absorption, the reduction rates of small capillary pores were 49.0% (50%BFS), 41.5% (pure cement), 20.2% (30%FA) and 13.0% (16%FA24%BFS). The self-healing performance of pastes with 50% BFS was most obviously improved that crack with width of 0.43 mm could be completely healed within 21d, while the relative water permeability coefficient dropped by around 80%, followed by pure cement, 30%FA and 16%FA24%BFS pastes. Notably, the morphology of the crack healing product in the blend pastes with FA and BFS was changed with the addition of CA, a large amount of lumpy and clustered calcite was generated, which promoted the compactness and content of healing products. The results of this study showed that CA could significantly improve pore structure, water transport and self-healing properties of high-volume BFS cementitious materials, which meant that CA had a better application prospect in high-volume BFS cement-based materials.

Effect of acid‐activation on CaO existential state and reactive properties of hot‐splashed steel slag in cement‐based materials

AbstractThe over‐burnt free‐CaO(f‐CaO) existential state in hot‐splashed steel slag is understood by observing the microstructure of steel slag section and analyzing the minerals in the steel slag (SS). In the investigation, a new method of using hydrochloric acid as the solvent to modify the steel slag powder (SSP) is put forward. The effects of hydrochloric acid pretreatment on the surface morphology of SS and the hydration activity and soundness of SSP blended cement are investigated. Furthermore, the failure mechanism of steel slag cement‐based materials and the hydration mechanism of acid‐activated steel slag (ASS) are discussed in detail. The research indicated that the optimum dosage of modified SSP is 20 wt%. At this dosage, the 7‐ and 28‐day compressive strength of paste is nearly increased 15% compared with the untreated steel slag cement‐based mortar specimens. Moreover, the acid activated SS‐blended cement pastes show much better soundness performances after autoclaved curing tests when compared with corresponding pastes with SS without treatment. It provides a promising approach for efficient and safe utilization of SS as supplementary cementitious material.

Compressed Earth Blocks Using Sediments and Alkali-Activated Byproducts

Sediment dredging is necessary and vital to preserve maritime activities and prevent floods. The management of these sediments represent an environmental challenge for many countries all over the world. This study focuses on evaluating the feasibility of using dredged sediments for the manufacturing of compressed earth blocks (CEB). The alternative construction material has the potential of reducing the need for dredged sediment onshore storage or ocean dumping. Several experimental tests have been conducted on two geopolymer types, which were obtained by mixing sediments from the northern region of France, fly ash (FA), and grounded blast furnace slag (GBFS). The geopolymers, which were activated using an eight-molar concentrated sodium hydroxide solution (NH), were cured at a temperature of 50 °C. The results have shown that a geopolymer content of 36% of FA and 10% of GBFS along with (NH) alkaline solution has significantly improved the mechanical properties of CEBs, which have outperformed those of Portland Cement-stabilized traditional blocks. The use of NH has resulted in the formation of crystalline calcium silicate hydrate (C-S-H) amorphous gel. Adding GBFS to the mix has enhanced the geopolymer paste compressive strength and microstructure because of the formation of additional C-S-H. The valorization of dredged sediments in CEB based on geopolymer stabilization can contribute to the reduction of the CO2 footprint of the construction industry.

Improvement of Calcium Aluminate Cement Containing Blast Furnace Slag at 50°C and 315°C

During the thermal recovery of heavy oil thermal recovery wells, improving the mechanical properties and integrity of the cement ring is of great significance for the safe and efficient exploitation of heavy oil resources. This paper studies the relative properties of calcium aluminate cement and three kinds of slags under the conditions of 50°C × 1.01 MPa and 315°C × 20.7 MPa. CAC-slag composite material performance was evaluated using the cement paste compressive strength and permeability tests to study the physical properties of CAC with blast furnace slag. X-ray diffraction analysis, scanning electron microscopy (SEM), and thermal analysis (DSC/TG) were carried out to investigate the mineralogical composition of CAC with blast furnace slag. Results show that adding blast furnace slag did not affect the performance of cement slurry. Moreover, C2ASH8 curing occurred at low temperature, the microstructure of CAC paste was compact, and the permeability resistance was improved, thus improving the low-temperature properties of neat CAC. When cured at a high temperature, the CAC paste was mainly hydrated with C3ASH4 and AlO(OH), which had a well-developed crystal structure. Adding blast furnace slag can improve the CAC resistance to high temperature.

Design of High Volume CFBC Fly Ash Based Calcium Sulphoaluminate Type Binder in Mixtures with Ordinary Portland Cement.

Growing concerns on global industrial greenhouse gas emissions have boosted research for developing alternative, less CO2 intensive binders for partial to complete replacement of ordinary Portland cement (OPC) clinker. Unlike slag and pozzolanic siliceous low-Ca class F fly ashes, the Ca- and S-rich class C ashes, particularly these formed in circulating fluidised bed combustion (CFBC) boilers, are typically not considered as viable cementitious materials for blending with or substituting the OPC. We studied the physical, chemical-mineralogical characteristics of the mechanically activated Ca-rich CFBC fly ash pastes and mortars with high volume OPC substitution rates to find potential alternatives for OPC in building materials and composites. Our findings indicate that compressive strength of pastes and mortars made with partial to complete replacement of the mechanically activated CFBC ash to OPC is comparable to OPC concrete, showing compared to OPC pastes reduction in compressive strength only by <10% at 50% and <20% at 75% replacement rates. Our results show that mechanically activated Ca-rich CFBC fly ash can be successfully used as an alternative CSA-cement type binder.

Comparative research on the effect of various mineral admixtures on the early hydration process of cement

Selection of mineral admixtures (MAs) was an effective way to reduce the rapid heat release of mass concrete at early ages, avoiding the cracks caused by the thermal stress. Herein, fly ash (FA), steel slag (SS) and ground granulated blast-furnace slag (GGBS) was used to replace cement with the dosage of 40%, and the early hydration process and microstructure evolution of specimens were investigated by hydration heat (HH), hydration temperature (HT), XRD, TGA and SEM. The experimental results indicated that the use of various MAs reduced the 3 d HH by 20–33%, owing to the reduction of cement content. The highest HT for cement-FA paste was decreased from 54 ℃ in cement paste to 37.0 ℃, whereas that for cement-SS paste and cement-GGBS paste was decreased to 38.4 ℃ and 39.8℃, especially including a constant temperature period at 15.62–18.14 h and 12.67–14.50 h. It was demonstrated that the reactivity of FA was greatly lower than that of SS and GGBS at early ages. Moreover, the early hydration degree of cement was increased by the dilution and nucleation effects, whereas the compressive strength of paste was reduced by 24–53% at 3 d. However, the compressive strength of cement-GGBS paste at 28 d was equivalent to that of cement paste, resulting from the continuous hydration of GGBS. These results provided the selection basis for MAs in mass concrete.

Effect of Fly Ash Belite Cement on Hydration Performance of Portland Cement

Fly ash belite cement is a green, low carbon cementitious material, mainly composed of hydraulic minerals of dicalcium silicate and calcium aluminate. In this study, we used fly ash belite cement to control the setting time, hydration heat, strength, composition and microstructure of hydration products in Portland cement. Results showed that incorporating fly ash belite cement into Portland cement can shorten the setting time, accelerate hydration reaction speed, enhance early hydration heat release rate of silicate minerals and reduce total hydration heat. Moreover, replacing composite cement with 30% FABC causes the 90 d compressive strength of pastes and mortars to reach 107 and 46.2 MPa, respectively. The mechanical properties can meet the requirements of P·F 42.5 cement. During the hydration reaction process, clinker and Portland cement have a synergistic hydration effect. Notably, hydration of fly ash belite cement promotes the formation of C-S-H gel, Ettringite and calcium hydroxide, thereby significantly enhancing long-term strength. With the increase of FABC contents, the long-term strength would be improved with the densification of hydration products. The porosity has a great influence on the strength, and the high porosity was the main cause of the low early strength of FABC pastes. FABC and its composite cement show promise for mass concrete applications and can be applied as a setting agent for Portland cement.

Effect of elevated temperature on polypropylene fiber reinforced alkali-activated high calcium fly ash paste

This paper examined the mechanism of polypropylene fiber (PP) reinforced alkali-activated high calcium fly ash paste (AHFP) exposed to high temperature. The PP was added into the AHFP mixture at the dosages of 0, 0.5, 1.0 and 1.5 % wt of fly ash. The 10 M (molar) NaOH, Na2SiO3/NaOH ratio of 2.0, and liquid/binder ratio of 0.60 were used. Compressive and flexural strengths, and microstructure of AHFP after exposed to 200, 400, 600 and 800 °C were studied. The results showed that the use of PP at 0.5 % wt of fly ash resulted in the best improvement in compressive strength of paste. For flexural strength, a slightly higher PP content at 1.0 % wt of fly ash was the optimum. For exposure to high temperature, the residual flexural strength was nearly one third at 400 °C and reduced to 8–12 % for temperatures beyond this. With the increasing exposed temperature, the air void and large capillary pore increased, but the medium capillary pore and gel pore reduced. The results indicated that the mechanisms of weight and strength losses of AHFP were due to thermo-hygral damage around 220−320 C, followed by thermo-mechanical damage at 430−660 C and thermo-chemical damage at 700 C onwards.