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Alkali-activated concretes (AACs) are attracting increasing attention due to their potential as alternatives to ordinary Portland cement concrete (OPCC). This paper is a holistic review of current research on the mechanical properties of AAC including research on its compressive strength, tensile strength, elastic modulus, Poisson’s ratio, stress–strain relationship under uniaxial compression, fracture properties, bond mechanism with steel reinforcement, dynamic mechanical properties, and high-temperature performance. Three types of AAC are reviewed: alkali-activated slag, alkali-activated fly ash, and alkali-activated slag-fly ash concretes. The applicability to AAC of design formulas found in codes of practice that were developed to estimate the basic mechanical performances of OPCC is also discussed. It is shown that, in general, AAC exhibits better bond performance with steel reinforcement and better strength performance after exposure to elevated temperatures than OPCC. For the other reviewed mechanical properties, the differences between AAC and OPCC largely depend on the proportions of raw materials in the concrete; specifically, the slag to fly ash ratio may be a very influential factor. As there is a trend to combine slag and fly ash in the production of AAC to achieve normal temperature curing and environmental friendliness, further research is deemed necessary to determine how the slag to fly ash ratio influences the fundamental mechanical properties of AAC and how this affects practical designs. [ABSTRACT FROM AUTHOR]

An experimental study into the axial compressive behaviour of concrete-filled circular hollow section (CHS) steel columns with internal fibre reinforced polymer (FRP) tubes is presented in this paper. A total of 17 concrete-filled steel tubular (CFST) columns were tested, 15 with an inner FRP tube and 2 with no inner tube. Complementary material tests and tests on 15 FRP-confined concrete (FCC) columns were also carried out. The varied test parameters included the concrete strength, the ratio of the diameter of the steel tube to that of the FRP tube, the diameter to wall thickness ratio of the inner FRP tube and the type (influencing principally the rupture strain) of the FRP. It was found that the presence of the inner FRP tube led to considerably improved axial compressive behaviour due to the greater levels of confinement afforded to the ‘doubly-confined’ inner concrete core; the load-bearing capacity was increased by between about 10% and 50% and the ductility was also enhanced. Greater benefits arose with (1) increasing diameter of the inner FRP tube due to the increased portion of the cross-section that is doubly-confined and (2) increasing wall thickness of the inner FRP tube due to the increased level of confinement afforded to the inner concrete core. The load-deflection responses of all tested specimens were reported, revealing that failure was generally gradual with no sharp loss in load-bearing capacity, implying that the embedment of the inner FRP tube within the concrete enables it to continue to provide a reasonable degree of confinement even after the initiation of fibre rupture; this is different to the sudden loss of confinement typically observed in FRP externally jacketed concrete columns. [ABSTRACT FROM AUTHOR]

The mechanistic insights into silico-aluminophosphate (SAP) geopolymer formation remain an enigma. Here, we aim to elucidate this process and improve the early-age performance of SAP geopolymers by utilizing incinerated sewage sludge ash (ISSA). Interestingly, phosphoric acid-ISSA interaction released Ca2+ and Al3+ ions from ISSA faster than the dealumination of metakaolin. These ions agglutinated with the active soluble (PO 4)3- units, evidenced by transmission electron microscopy (TEM), enhancing the early-age compressive strength of ISSA-incorporated SAP geopolymer binders. In contrast, the later strengths were relatively similar to the reference. Such binders had primary silico-alumino-phosphate (S-A-P) gels, possibly intimate with calcium-phosphate (C-P) and alumino-phosphate (A-P) gels, improving the micromechanical properties of the binder. The elastic moduli of these gels lay between 23–25 GPa, higher than conventional N-A-S-H gels. Furthermore, ISSA switched the chemistry of reaction products by favoring Al IV -OP units over Al VI -OP units in SAP geopolymers, even though the Si environment remained unchanged, as confirmed by NMR. • Formation mechanism of SAP geopolymer with and without ISSA is reported. • ISSA addition enhanced the early-age compressive strength of SAP geopolymer. • ISSA reduced the phosphoric acid in the SAP geopolymers by up to 28% by weight. • The mechanisms that govern such observations are discussed in detail. [ABSTRACT FROM AUTHOR]

• ECC using artificial fine aggregates were developed for the first time. • The developed high-strength ECC incorporating geopolymer and cement-bonded artificial fine aggregates achieved a compressive strength of 122.4 and 120.9 MPa, respectively. • Among the existing ambient-cured high-strength ECC, the developed geopolymer aggregate ECC recorded the highest tensile strain capacity (9.0%). • For high-strength ECC, the use of geopolymer artificial fine aggregate resulted in more saturated multiple cracking. In this study, Engineered/Strain-Hardening Cementitious Composites (ECC/SHCC) using artificial fine aggregates [i.e., geopolymer aggregates (GPA) and cement-bonded aggregates (CBA)] were developed for the first time. The developed GPA-ECC and CBA-ECC showed a compressive strength over 120 MPa, and the GPA-ECC recorded the highest tensile strain capacity (9.0%) among the existing ambient-cured high-strength ECC in literature. Compared with fine silica sand ECC (FSS-ECC) as a control mix, GPA-ECC and CBA-ECC showed lower compressive and tensile strength, owing to their lower aggregate strengths. From digital image correlation analysis, a more saturated multiple cracking behavior was observed for GPA-ECC as compared to CBA-ECC and FSS-ECC. In addition, the use of artificial aggregates had marginal effect on the crack width distribution of high-strength ECC. The findings in this study demonstrate the feasibility of using artificial fine aggregates in ECC production and provide a new avenue to improve ductility and sustainability for ECC materials. [ABSTRACT FROM AUTHOR]

• An artificial intelligence-based gene expression programming approach was used for modelling the performance of bio-composites. • Mathematical models were proposed for density, compressive strength and thermal conductivity of bio-composites. • Performance of the proposed mathematical models was validated using statistical parameters and performance indices. • The proposed models depicted high degree of generalization capability and predictability. Giving the high amount of carbon and energy emission from the use of traditional building materials, the use of bio-composites made from industrial crops especially hemp has caught attention from researchers in recent years. These bio-composites not only enhance the thermal performance of buildings but also promote sustainable development due to their eco-friendly nature. Due to their highly heterogeneous nature, however, most of the existing studies on the bio-composites have only focused on experimental investigations, while mathematical modeling of physical, thermal and mechanical properties of bio-composite remains a challenge for the researchers. In this paper, an artificial intelligence (AI) based gene expression programming (GEP) technique is used to develop the mathematical models for predicting the dry density, compressive strength and thermal conductivity of hemp-based bio-composites. A large amount of database was established based on past studies and the most influential parameters were identified by several trial analyses. The proposed mathematical models showed a high correlation with the experimental results. All the models passed the statistical and performance index checks showing strong predictability, generalization capability and high accuracy of GEP-AI models. Comparison of results with the regression analysis techniques further proved the superiority of GEP-AI models over the traditional methods. [ABSTRACT FROM AUTHOR]

One of the major problem in ultra-high-performance concrete (UHPC) after exposure to high-temperatures is explosive spalling. Adding a single type of fibers alone is insufficient sometimes for suppressing such spalling, and therefore, hybridization of fibers has been adopted, particularly steel with organic fibers. However, the degradation of organic fibers at ambient and elevated temperatures is a significant challenge in the long term and needs to be addressed. Recently, inorganic basalt fibers have been considered as an alternative to organic fibers due to their better mechanical strength and high-temperature resistance characteristics. In this study, hybridizing steel with basalt fiber is proposed as a potential solution to the aforementioned problem. The spalling behavior, residual compressive strength, microstructure, porosity, hydration kinetics, phase decomposition, and quantification of hydration products were evaluated for hybrid steel-basalt fiber reinforced UHPC after exposure to high-temperatures. The study results indicated that hybrid steel-basalt fiber reinforced UHPC successfully prevented explosive spalling behavior. The use of inorganic mineral basalt fibers offers a promising solution for developing UHPC with superior high-temperature resistance. • The study explored the possibility of hybridizing steel with basalt fibers in UHPC. • This study investigates the effects of high-temperature exposure on the properties of UHPC. • Basalt fibers were considered due to their high-temperature resistance characteristics. • A hybrid of steel with basalt fibers in UHPC could be an effective approach for preventing spalling. [ABSTRACT FROM AUTHOR]

• Polycarboxylate is the most effective superplasticizer for Ca(OH) 2 /Na 2 SO 4 geopolymer. • Reducing the w/b ratio improves the compressive strength of Ca(OH) 2 /Na 2 SO 4 geopolymer. • Lowering the w/b using high superplasticizer content (i.e. 3%) delays the participation of reaction products. This paper investigates the effect of three different superplasticizers (SPs), Naphthalene (N), Melamine (M) and Polycarboxylate (PC), on the properties of one-part fly ash/slag geopolymer pastes activated by Ca(OH) 2 /Na 2 SO 4 powder combination. The flowability, setting time, and compressive strength of the achieved geopolymer pastes were assessed. It was found that the superplasticizers significantly improved the flowability, retarded the setting time, and increased the compressive strength of the one-part Ca(OH) 2 /Na 2 SO 4 geopolymer pastes. The most recommended superplasticizer was found to be polycarboxylate. The use of polycarboxylate SP for decreasing the water content (i.e. w/b) in Ca(OH) 2 /Na 2 SO 4 geopolymer pastes has resulted in reducing the porosity and enhancing the compactness of the aluminosilicate gel, therefore, improved the compressive strength. It was found that the excessive use of polycarboxylate (i.e. 3%) for additional water reduction in Ca(OH) 2 /Na 2 SO 4 geopolymer pastes had an adverse effect; it extended the induction period and delayed the participation of reaction products, thus significantly prolonged the setting time. Furthermore, a comparison between the achieved Ca(OH) 2 /Na 2 SO 4 geopolymer pastes and the conventional Na 2 SiO 3 -anhydrous one-part geopolymer pastes was carried out. It was found that Ca(OH) 2 /Na 2 SO 4 geopolymer exhibited significantly lower compressive strength, higher flowability and considerably longer setting time compared to Na 2 SiO 3 geopolymer. Hence, such binder can be implemented as a green non-structural material. [ABSTRACT FROM AUTHOR]

CO 2 capture and utilization is an important environmental protection measure to reduce greenhouse gas (GHG) emissions. In order to realize the carbon fixation of cement and optimize the performance of foam concrete, ordinary Portland cement (OPC), fly ash (FA), CO 2 gas and animal protein foaming agent were used as the main raw materials to prepare CO 2 foam concrete (CFC). The diffusion principle of CO 2 gas in the bubble was analyzed and the performance of CFC was investigated by testing the mechanical, thermal, water absorption and drying shrinkage properties, and microscopic characterization. The results showed that the compressive strength of CFC with 20% CO 2 volume could reach 3.32 MPa, which was 24.8% higher than that of the control group (2.66 MPa), and the 70d drying shrinkage rate of CFC was 2.56 mm/m, which was 23.1% lower than that of the control group (3.33 mm/m). The thermal conductivity and water absorption of CFC were also reduced. XRD analysis revealed that intensity of CaCO 3 was enhanced with the increase of CO 2 gas content in the bubble. SEM analysis also corroborated the XRD results and a large number of CaCO 3 crystals were observed in the samples of different ages with the increase in CO 2 concentration, which enhanced the density of C-S-H gel pores and refined the microstructure. [ABSTRACT FROM AUTHOR]

• Effectiveness of calcium aluminate cement (CAC) was identified under high temperatures. • A comparative study with ordinary Portland cement (OPC)-based UHPC was performed. • An efficient CAC-based UHPC was developed without explosive spalling. • Thermo-mechanical properties were studied under high temperatures. • Mechanisms of spalling resistance and thermo-mechanical properties were explored. Conventional ordinary Portland cement (OPC)-based UHPC is vulnerable to explosive spalling under high temperatures. This study aims to classify the role of calcium aluminate cement (CAC) as the substitution for OPC in UHPC under high temperatures and finally develop an efficient UHPC without explosive spalling. It was found that CAC-based UHPC (UHPC-CAC) and OPC-based UHPC (UHPC-OPC) reached their peak strength both at 250 °C, but the peak strength (153.8 MPa) of UHPC-CAC was higher than that (137.5 MPa) of UHPC-OPC. Explosive spalling was found in UHPC-OPC after reaching 500 °C, while no spalling was observed in UHPC-CAC even at 1000 °C. The effectiveness of CAC in reducing the mechanical degradation and preventing the spalling of UHPC was attributed to three potential mechanisms: (1) CAC had less physically bound water to cause the vapor pressure in UHPC; (2) The main hydration product (i.e., calcium aluminosilicate hydrates) decomposed to a lesser extent, compared to the hydration product (i.e., calcium silicate hydrates) of OPC, as proved by X-ray diffraction (XRD) analysis, Thermogravimetric analysis (TGA), and Fourier-transform infrared (FTIR) analysis; (3) there exists pores coarsening in UHPC-CAC, as evidenced by micro-XCT, which could release the water pressure in UHPC and thus prevent the spalling at elevated temperatures. [ABSTRACT FROM AUTHOR]

In this study, seawater sea-sand Engineered Geopolymer Composites (SS-EGC) were developed and investigated for the first time. The developed EGC achieved high compressive strength (over 140 MPa) and high tensile ductility (around 8%) simultaneously. Emphasis was placed on understanding the influence of seawater and sea-sand (compared to freshwater and washed sea-sand) on the matrix properties and tensile performance of EGC, with two fly ash-to-slag ratios (8:2 and 2:8) considered in the matrices. Results showed that the use of seawater hindered the reaction of EGC matrix and led to a slight reduction of compressive strength (compared to the freshwater counterpart). It was found that the content of hydrotalcite phases in SS-EGC matrix was higher than that of freshwater EGC. In addition, using seawater was found to increase the average modulus of matrix obtained from nanoindentation, leading to a higher fiber/matrix bond strength. The tensile strain capacity of SS-EGC was slightly lower than that of freshwater EGC. The developed SS-EGC showed superior crack resistance and better sustainability than the cement-based counterpart from the literature (with similar compressive strength). The findings of this study provided useful knowledge for the design and development of high-strength high-ductility SS-EGC towards sustainable and resilient marine infrastructures. • Seawater Sea-sand EGC (SS-EGC) were developed and investigated for the first time. • Using seawater and sea-sand slightly decreased the compressive strength of EGC. • The content of hydrotalcite phases in SS-EGC matrix was higher than that of freshwater EGC. • Using seawater and sea-sand in EGC increased the tensile strength but lowered the tensile strain capacity. • The developed SS-EGC showed better sustainability and lower cost than the cement-based counterpart in the literature. [ABSTRACT FROM AUTHOR]

This study designed and developed strain-hardening alkali-activated fly ash/slag composites (SH-AAFSC) with both ultra-high compressive strength and ultra-high tensile ductility for the first time. The developed SH-AAFSC showed a compressive strength of 94.4–180.7 MPa and a tensile strain capacity of 8.1–9.9 %, which successfully pushed the performance envelope of alkali-activated materials. A multi-scale investigation was conducted to get an in-depth understanding of the obtained mechanical properties. Results showed that higher GGBS content increased the Ca/Si ratio of C(N)ASH, leading to a further refined microstructure with reduced porosity. As w/p ratio decreased from 0.27 to 0.22, the compressive strength significantly increased but the tensile ductility slightly decreased. Notably, a strong linear relationship was observed between fiber-bridging strength and the average elastic modulus of matrix obtained from nanoindentation. The study provided an avenue to produce SH-AAFSC towards ultra-high compressive strength and tensile ductility, which are promising for resilient and sustainable infrastructures. [Display omitted] • SH-AAFSC with ultra-high compressive strength (180.7 MPa) and tensile ductility (9.1 %) were designed for the first time. • Increasing GGBS dosage from 20 % to 80 %, the tensile strength and ductility of SH-AAFSC decreased first and then increased. • Lower water-to-precursor ratio resulted in an increased compressive strength but a decreased tensile ductility of SH-AAFSC. • A strong linear relationship was observed between fiber-bridging strength and the average elastic modulus of SH-AAFSC matrix. • The developed SH-AAFSC successfully pushed the performance envelope of alkali-activated concrete. [ABSTRACT FROM AUTHOR]

Ultra-High-Strength Engineered Cementitious Composites (UHS-ECC) incorporating artificial geopolymer aggregates (GPA) were developed and over-saturated cracking (i.e., average tensile crack spacing smaller than the theoretical limit) was observed in this novel material. The developed UHS-ECC exhibited an ultra-high compressive strength (over 150 MPa) and an ultra-high tensile ductility (over 8%) simultaneously. The influences of GPA size on the matrix properties, tensile performance, micromechanics, and cracking behavior of UHS-ECC were systematically investigated. Over-saturated cracking and double-stage crack evolution (i.e., a bilinear relation between average crack width and tensile strain) were observed in UHS-ECC with GPA size smaller than 0.60 mm, while saturated cracking and single-stage crack evolution (i.e., a linear relation between average crack width and tensile strain) were observed in the other groups. Finally, the mechanism of over-saturated cracking and double-stage crack evolution was illustrated. The findings of this study extend the fundamental knowledge of ECC technology, which is meaningful for designing and developing UHS-ECC materials towards ultra-high tensile ductility. [Display omitted] • GPA-based UHS-ECC were developed with both ultra-high strength (over 150 MPa) and ultra-high ductility (over 8%). • Over-saturated cracking was observed in UHS-ECC with GPA size smaller than 0.60 mm. • UHS-ECC with over-saturated cracking exhibited a double-stage crack evolution. • The mechanism of the over-saturated cracking of the GPA-based UHS-ECC is revealed. • UHS-ECC with GPA size of 0.30–0.60 mm exhibited the highest strain-hardening potential. [ABSTRACT FROM AUTHOR]

• Mineral wollastonite microfiber is a low-cost and sustainable reinforcement for 3DCP. • At 10% replacement of wollastonite, the static yield stress and thixotropy were enhanced. • At 10% replacement of wollastonite, the flexural strength was enhanced. • At 10% replacement of wollastonite, the compressive strength was not changed. Integration of reinforcement in the 3D concrete printing (3DCP) process is a major challenge. As a possible solution, the addition of short synthetic/metallic fibers directly to a fresh mixture before extrusion has been investigated in previous studies. However, the use of natural/inorganic microfibers such as wollastonite as reinforcement for 3DCP has received less attention. Wollastonite is substantially cheaper and more environmentally friendly than synthetic/metallic fibers. To fill this knowledge gap, this study reports a systematic approach to enhance the flexural strength of a 3D-printed geopolymer by the addition of wollastonite microfiber. The effect of different replacement levels of wollastonite (0, 5, 10, 15, 20, and 30% by weight of sand) on setting time and mechanical properties of several mixtures were evaluated to identify the optimum wollastonite content. The printing performances, rheological properties, and mechanical strengths of the optimum mixture were then evaluated and compared with the control mixture (without wollastonite). The results showed that at 10% replacement level, the static yield stress and thixotropy property of the mixture were enhanced, which is desirable for the superior printability of the mixture. In addition, the flexural strength of the mixture incorporating 10% wollastonite was superior to the control mixture, whereas the compressive strength was not changed. The use of mineral wollastonite microfibers as a low-cost and environmentally friendly reinforcement for 3DCP is experimentally established in this study. [ABSTRACT FROM AUTHOR]

It is well known that an increase in the compressive strength of cementitious composites is usually accompanied by a loss of tensile ductility. Designing and developing ultra-high-strength cementitious composites (e.g., ≥200 MPa) with high tensile strain capacity (e.g., ≥3%) and excellent crack resistance (e.g., crack width ≤100 μm) remain challenging. In this study, a series of ultra-high-strength Engineered Cementitious Composites (UHS-ECC) with a compressive strength over 210 MPa, a tensile strain capacity of 3–6% (i.e., 300–600 times that of ordinary concrete), and a fine crack width of 67–81 μm (at the ultimate tensile strain) were achieved. Hybrid design of fiber reinforcement and matrix for UHS-ECC was adopted by combining the ECC and ultra-high-performance concrete (UHPC) design concepts, and the effect of fiber hybridization and aspect ratio on the mechanical behavior of UHS-ECC was comprehensively investigated. The overall performance of UHS-ECC was assessed and compared with the existing high-strength ECC and strain-hardening UHPC, and it was found that the currently designed UHS-ECC recorded the best overall performance among the existing materials. Finally, the multiple cracking behavior of UHS-ECC was analyzed and modeled based on a probabilistic approach to evaluate its critical tensile strain for durability control in practical applications. The results of this study have pushed the performance envelope of both ECC and UHPC materials and provided a basis for developing cementitious composites with simultaneously ultra-high compressive strength, ultra-high tensile ductility, and excellent crack resistance. [Display omitted] • Hybrid design of fiber reinforcement and matrix for UHS-ECC was introduced by combining the UHPC and ECC design concepts. • UHS-ECC with a compressive strength over 210 MPa and a tensile ductility over 6% was developed. • UHS-ECC with 2% 18-mm PE fiber and 1% 13-mm steel fiber recorded the best overall performance. • Cracking behavior was modeled by a probabilistic approach to estimate the critical tensile strain of UHS-ECC. [ABSTRACT FROM AUTHOR]

In this study, a novel form of tubular permanent formwork that is made of ultra-high-performance concrete (UHPC) internally reinforced with fiber-reinforced polymer (FRP) micro-bars (herein referred to as FRP-UHPC tubular permanent formwork or simply FRP-UHPC tubular column) is developed. The axial compression test results of FRP-UHPC tubular columns with and without in-filled concrete are presented and discussed. Effects of the FRP micro-bar spiral pitch, the steel fiber addition in the UHPC, the tube thickness and the presence of external FRP confinment are investigated. The test results confirmed that the FRP-UHPC tubular columns have an excellent compressive strength, and the strength and ductility of existing concrete columns jacketed with an FRP-UHPC composite tube are substantially enhanced due to the confinement and axial contribution of the FRP-UHPC tube. The proposed FRP micro-bar-reinforced UHPC composite tubes are attractive in structural applications as pipelines or permanent formworks for columns, as well as external jackets (can be prefabricated in the form of two halves of composites tubes) for strengthening deteriorated reinforced concrete columns. [ABSTRACT FROM AUTHOR]

In this study, Engineered/Strain-Hardening Cementitious Composites (ECC/SHCC) incorporating geopolymer fine aggregates were successfully developed with high strength and high ductility. A multi-scale investigation was conducted to gain an in-depth understanding of the microstructure and ductility enhancement mechanism of geopolymer aggregate ECC (GPA-ECC). The use of geopolymer fine aggregates enabled the high-strength ECC to achieve higher tensile ductility and finer crack width compared to existing ones with similar compressive strength in the literature. It was found that the GPA reacted with the cementitious matrix, and the width of the GPA/matrix interfacial transition zone (ITZ) was larger than that of the silica sand/matrix ITZ. Moreover, the GPA achieved a strong bond with the cementitious matrix and could behave as "additional flaws" in high-strength matrix, resulting in saturated multiple cracking and excellent tensile ductility of ECC. This study provides a new avenue for developing high-performance fiber-reinforced cementitious composites based on artificial geopolymer aggregates. • Geopolymer fine aggregates were successfully applied to develop high-strength high-ductility ECC with fine crack width. • Geopolymer fine aggregates reacted with cementitious paste, resulting in a strong interfacial bond. • Geopolymer fine aggregates acted as "additional flaws" in high-strength ECC matrix, leading to saturated multiple cracking. • Compared with existing ambient-cured high-strength ECC, geopolymer aggregate ECC exhibited superior tensile ductility. [ABSTRACT FROM AUTHOR]

Abstract: This paper aims to investigate the durability properties of recycled aggregate concrete treated with silane-based water repellent agents, since the high water absorption of recycled aggregate concrete is a major factor jeopardizing its durability. Different dosages of silane-based water repellent agents were either coated on the surface of the concrete (hereafter “surface silane treatment”) or integrally added into the concrete mixture (hereafter “integral silane treatment”). The mechanical and durability properties of the treated concrete were evaluated. It was found that integral silane treatment can improve the durability of recycled aggregate concrete, but may lead to reductions in compressive strength; surface silane treatment is more effective in improving the resistance of recycled aggregate concrete to capillary water absorption, carbonation and chloride penetration than integral silane treatment. [Copyright &y& Elsevier]

The production method of geopolymer lightweight aggregates (GLAs) is explored in this study through crushing technique, which has a good prospect for massive industrial production. Geopolymer cubes with the dimension of 100 mm × 100 mm × 100 mm were firstly produced using one-part geopolymer technology and then crushed into coarse aggregates with angular shapes. Coal fly ash (FA), ground granulated blast-furnace slag (GGBS) and anhydrous sodium metasilicate particles in industrial grades were utilized for the one-part geopolymer in this study. Results showed that the produced GLAs with different mixes were all lightweight with a loose bulk density below 800 kg/m3 and an apparent density of 1450–1750 kg/m3. The produced GLAs were further used as coarse aggregates to produce geopolymer aggregate concrete (GAC). It was found that for GLAs, the increase in alkalinity and the addition of GGBS resulted in a higher one-day compressive strength, which would make better aggregate shapes, but need higher crushing energy and might cause initial damage to the aggregates. The highest cylinder compressive strength was obtained in GLAs with pure fly ash as the precursor and the activator to precursor ratio of 14%. However, the highest compressive strength of geopolymer aggregate concrete (GAC) was obtained using GLAs with 20% GGBS addition and the activator to precursor ratio of 12% although the cylinder compressive strength of this type of aggregates was not the highest. It was found that the addition of GGBS in GLAs resulted in stronger aggregate-matrix interface in GAC. Finally, the embodied carbon and material cost of GLAs were analyzed. The findings in this study are useful for future production and application of GLAs in concrete industry. • Geopolymer lightweight aggregates (GLAs) were produced using one-part geopolymer technology and crushing method. • Geopolymer aggregate concrete (GAC) was produced using GLAs. • The effects of geopolymer mix proportions on the GLAs and lightweight GAC were investigated. • The GLA-mortar matrix interface in GAC was characterized in details. • A 4-dimensional representation was introduced for assessing the overall performance of GLAs. [ABSTRACT FROM AUTHOR]

Engineered Cementitious Composite (ECC) is an advanced fiber-reinforced concrete exhibiting multiple-cracking and strain-hardening under tension. This study aims to explore the feasibility of producing high-strength seawater sea-sand Engineered Cementitious Composites (SS-ECC) for marine and coastal applications facing the shortage of freshwater and river/manufactured sand. The effects of key composition parameters including the sea-sand size (1.18/2.36/4.75 mm), the polyethylene fiber length (6/12/18 mm), and the fiber volume dosage (1.0/1.5/2.0%) on the mechanical performance of SS-ECC were comprehensively investigated. SS-ECC with tensile strength over 8 MPa, ultimate tensile strain about 5%, and compressive strength over 130 MPa were achieved. Using seawater and sea-sand had almost no negative effects on the 28-day mechanical properties of high-strength ECC. For SS-ECC, increasing fiber length and dosage enhanced the tensile strain capacity, and sea-sand size had limited effects on the tensile performance; these phenomena were interpreted by the micromechanical analysis. A probabilistic-based method was proposed to analyze the reliability of the tensile strain capacity of SS-ECC, and it showed good agreement with the experimental results. The findings provide new insights into the design and applications of ECC in marine and coastal infrastructures for improving safety, durability, sustainability, and reliability. • SS-ECC with compressive strength >130 MPa for marine and coastal applications was developed. • High-strength SS-ECC achieved tensile strength >8 MPa and tensile strain capacity about 5% at 28 days. • Using seawater had almost no negative effects on the 28-day mechanical properties of high-strength ECC. • The effects of sea-sand size, fiber length and fiber dosage on mechanical properties were investigated. • A probabilistic-based model was proposed to analyze the reliability of tensile strain capacity of ECC. [ABSTRACT FROM AUTHOR]

In this study, the concept of "full-volume fly ash (FVFA) geopolymer mortar" is proposed using FA geopolymer as a binder and sintered fly ash aggregates (FAAs) to fully replace the conventional river sand (by volume), aiming to conserve natural sand resources through further utilizing of FA. The influences of the FAAs, the alkali concentration, and curing regime on the physical, mechanical, microstructure, and mineralogy properties of the FVFA geopolymer mortars were experimentally evaluated. The properties of the conventional river sand control mortars were used as a benchmark reference. The results indicated that both compressive strength and density of the FVFA geopolymer mortars were relatively lower compared to that of the control mortars. The change of alkali concentration and steam-curing duration could generate a wide variant range of the compressive strength and density. Further, the FVFA geopolymer mortars were found to have much higher total porosity relative to the control mortars. The drying shrinkage of the FVFA geopolymer mortars was much lower than that of control mortars due to the internal curing effect of the FAAs. It was challenging to identify the interfacial transition zone (ITZ) between the sintered FAAs and the FA geopolymer binder relative to that between sand and paste in control mortars. It was found that the external layer of the FAAs has reacted with the alkaline solution while the internal core remains relatively stable during the 28 days. • The concept of "full-volume fly ash (FVFA) geopolymer mortars" is proposed. • FVFA mortars achieved slightly lower compressive strength relative to sand mortars. • Densities of FVFA mortars were relatively lower than those of sand mortars. • Drying shrinkage of FVFA mortars was lesser compared to sand mortars. • ITZ of FVFA mortar was not clear due to the reaction of FAA with the activator. [ABSTRACT FROM AUTHOR]