Abstract ：

The complex design parameters and lack of standard mix design methods generate a difficulty in the high efficiently preparation of alkali-activated foamed geopolymer (AAFG). Therefore, this paper proposes an innovative intelligent design method of AAFG based on machine learning (ML) and Metaheuristic Optimization Algorithms (MOA). The effects of twelve factors on drying density (DD) and compressive strength (CS) of AAFG are revealed. The DD and CS predictive models of AAFG with high accuracy (R2 = 0.96 and 0.84) and strong generalization are trained through Random Forest (RF). The enlargements of proportions of granulated blast furnace slag (GBFS) and metakaolin (MK) in precursors can improve the CS but are not conducive to reduction of DD. Higher proportion of fly ash (FA) in precursors can efficiently reduce DD but can weaken the CS. Higher or lower Na2O content, silicate modulus (Ms) and water to binder (W/B) can reduce DD and CS with the optimal foaming conditions of 20 %, 1.0 and 0.75. More additions of foaming agents and foam stabilizers can reduce DD, while the CS has a remarkable degradation. Higher or lower foaming temperature (FT) is both not beneficial for the reduction of DD and enhancement of CS with the optimal FT of 60 degrees C. The intelligent design system of AAFG developed by RF and Slime Mould Algorithm (SMA) has easy operability, high efficiency, and good stability. The optimal preparation parameters can be efficiently acquired and the corresponding performances can be quickly and accurately predicted.

Keyword ：

Intelligent optimization design Performance prediction Alkali -activated foamed geopolymer

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Abstract ：

The long-term durability of basalt fiber-reinforced geopolymer concrete (BFRGC) in marine environments is importance for the development of sustainable construction practices. This study examines the long-term durability of basalt fiber-reinforced geopolymer concrete exposed to dry-wet cycles and immersion treatment in marine conditions. A geopolymer concrete with 1% fiber content was prepared and subjected to dry-wet cycles and immersion treatments in a 5% sulfate solution (Tehmina et al., 2014; Nasir et al., 2016; John et al., 2016) [13]. Density measurements, ultrasonic pulse velocity tests, and uniaxial compression tests were conducted on the BFRGC after various treatment durations. The mechanical properties of BFRGC were compared with geopolymer concrete without fibers in marine environments. Additionally, the changes in compressive strength of geopolymer concrete with and without fibers in different immersion environments were further discussed. Using low-field nuclear magnetic resonance (LF-NMR) technology, the variations in pore structure were also analyzed. The results show that the mechanical property loss from dry-wet cycles was greater than from immersion treatment. In BFRGC, strength decreased by 10.1% after 192 days of dry-wet cycles, compared to a smaller decrease of 5.6% in immersion environments. The inclusion of basalt fibers effectively enhances stability. When in dry-wet cycle tests, BFRGC strength decreased from 49.6 MPa to 44.6 MPa, a reduction of 10.1%. Conversely, geopolymer concrete without fibers dropped from 49.7 MPa to 42.1 MPa, a reduction of 15.5%. LF-NMR test results show that the porosity of geopolymer concrete without fibers increased by 21.6% and 17.5% in dry-wet cycles and immersion environments, respectively. In contrast, the porosity of BFRGC increased by 16.1% and 12.7%.

Keyword ：

Pore structure Geopolymer concrete Marine erosion Basalt fiber

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Abstract ：

To facilitate the use of geopolymer materials in shotcrete applications, this study presents the development of a geopolymer mortar and explores its flowability and early-stage mechanical properties. Firstly, 15 groups of geopolymer mortar specimens with 3 liquid-binder ratios (0.70, 0.75 and 0.80) and 5 binder-aggregate ratios (0.225, 0.250, 0.275, 0.300 and 0.325) were developed. Secondly, the P-wave velocity, slump, early-age compressive strength and compressive strength were obtained by ultrasonic pulse velocity test, slump test and uniaxial compressive test. Thirdly, discussion on the effect of liquid-binder ratio and binder-aggregate ratio on Pwave velocity, flowability, compressive strength and early-age compressive strength of geopolymer mortar were carried out. Finally, an optimal mix proportions rang of geopolymer mortar materials that meet the requirements of wet shotcrete technology were proposed. The results show that P-wave velocity, slump, early-age compressive strength and compressive strength increase as the increasing of liquid-binder ratio. The slump, compressive strength and P-wave increase as the increasing of binder-aggregate ratio. Moreover, the optimal binder-aggregate ratios were proposed as 0.244 - 0.321, 0.228 - 0.298, and 0.209 - 0.241 for geopolymer mortar with a liquidbinder ratio of 0.70, 0.75 and 0.80, respectively. Geopolymer mortar in these mix proportions achieves compressive strengths ranging from 28.4 MPa to 41.1 MPa after curing for 1 day and 44.2 MPa to 55.4 MPa after curing for 28 days. The mix proportion of geopolymer mortar proposed in this paper can simultaneously meet the standard requirements for mechanical properties and flowability, demonstrating potential for wet shotcrete applications.

Keyword ：

Shotcrete application Binder-aggregate ratio Liquid-binder ratio Optimal mix proportion range Geopolymer mortar

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Abstract ：

This paper studied the effects of microwave power and time on microstructure and mechanical properties of Ultra -High Performance Geopolymer Concrete (UHPGC) matrix. Results show that conducting microwave treatment at curing age of 3d is suitable, the optimal microwave power and time are 560 W and 180 s with the 3d compressive strength and flexural strength of 125.4 MPa and 6.0 MPa. The large amount of heat generates in UHPGC matrix under microwave field, which leads to the increase in temperature within the UHPGC matrix. Due to hydration promotion caused by internal temperature rise, the tighter gels accumulation and lower porosity can be observed, which results in the remarkable improvement of compressive strength. However, microwave heating causes higher proportion of large pores and more generation of "melon seed flake" hybrid crosslinking products mainly including N -A -S -H, which will result in the reduction of flexural strength. Moreover, microwave pre -curing is more suitable for preparing UHPGC compared with the oven pre -curing comprehensively considering the early age compressive strength enhancement and energy consumption.

Keyword ：

Mechanism analysis Microwave pre -curing Geopolymer concrete Ultra -High Performance Mechanical properties

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Abstract ：

Waste sludge is a typical solid waste generated during construction excavation, which needs innocuity treatment and resource utilization. The development of geopolymer pavement base material using waste sludge is an economic and environmental method to realize the utilization of waste sludge. This manuscript aims to develop a geopolymer pavement base material using waste sludge and further evaluate its water stability under water soaking environment. The geopolymer specimens with different slag and waste sludge contents were prepared. The optimum mix proportion of geopolymer was determined by analyzing the effect of slag content on the ultimate compressive strength (UCS) and elastic modulus. The CO2 emissions and energy consumption of geopolymer was analyzed. The water stability of the geopolymer was further evaluated by analyzing the effects of soaking time on the density, wave velocity, mechanical properties and pore structure. The results show that the geopolymer with 50% slag content has the largest UCS and excellent strength development characteristics. The UCS of geopolymer pavement base material reaches 48.4 MPa and the CO2 emissions and energy consumption were reduced by 58.34% and 88.16% compared to C40 ordinary concrete. The results also show that the density, longitudinal wave velocity and porosity remain stable as soaking time increases. During the soaking process, the proportion of gel pores and transition pores decreases, while the proportion of capillary pores and air pores increases. The UCS of geopolymer pavement base material remains above 40 MPa after soaking for 90 days, showing excellent water stability. The geopolymer pavement base material has the potential application prospect in road engineering and emission reduction, which provides a feasible and cost-effective method for the utilization of waste sludge.

Keyword ：

Water stability Geopolymer Pore structure characteristics Waste sludge Low-field nuclear magnetic resonance

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Abstract ：

The efflorescence problem is always an intractable problem for geopolymer. Silica fume (SF), nano-silica (NS), 5A zeolite (ZL) and nano-silica treated with silane (NST), were used to mitigate the efflorescence of fly ash (FA) granulated blast furnace slag (GBFS) - steel slag (SS) based geopolymer. The effect of their dosages on the efflorescence was evaluated through accelerated efflorescing, leaching and unconfined compressive strength (UCS) tests. The inhibition mechanisms were explored by XRD, SEM, FTIR and MIP characterization. It revealed that SF and NS presented the most effective mitigating effect on efflorescence, with 9 % of SF and 2 % of NS totally inhibiting efflorescence and improving the compressive strength, and ZL and NST also alleviated the efflorescence at appropriate contents. Optimizing pore network and stabilizing free alkali were found to be the most important aspects for inhibiting efflorescence. The SF and NS worked efficiently in both two ways, which contained a large amount of dissolvable silicate that reacted with the excessive alkali to form C(N)-A-S-H and CS-H gels. This filled and reduced the pores from 26 nm to less than 10 nm, and stabilized alkali with reduce the free w(Na+) by more than 50.45 %. On the other hand, ZL can solidify free alkali through the ion exchange property and fill pores due to its microaggregate nature, and NST reduced the efflorescence through blocking free alkali migration paths by hydrophobicity of the pores. These findings would guide the selection of appropriate methods to solve the efflorescence problem of geopolymers.

Keyword ：

Nano-silica Steel slag Silica fume Geopolymer Efflorescence mitigation

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Abstract ：

The utilization of waste rubber as aggregates shows both environmentally friendly features and high costefficiency in construction, but may cause poor workability such as rubber flotation and agglomeration. To address the above issues, the pelletization method was adopted to produce rubberized artificial geopolymer aggregates (R-GPA), and the effects of different rubber modification methods and rubber contents were investigated through pelletization technologies, mechanical tests, X-ray computed tomography (XCT) and backscattered electron with energy-dispersive spectroscopy (BSE-EDS). Results showed that the combined modification with NaOH solution and silane coupling agent presented the most effective surface modification efficiency. According to microscopic analysis, rubber modification could effectively enhance the rubber-matrix interface. The produced R-GPA could thus possess an oven-dried particle density within 1500-1800 kg/m3, a water absorption of 7%-10.5%, and a pelletization efficiency over 98%, which provided a new insight into the value-added utilization of waste rubber and the promotion of artificial aggregate technologies.

Keyword ：

Surface modification Interface Pelletization Rubber Alkali-activated materials Geopolymer aggregates (GPA)

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Abstract ：

The evolution of globalization and rapid industrialization, coupled with intensive human activities, leads to a significant release of acidic gases and particles (e.g., NOX and SO2) is unavoidable. These emissions eventually result in dry and wet acid depositions due to atmospheric circulation. This infiltration of acidic elements alters the chemical properties of water systems, thereby deteriorating ground stability. The economically developed soft clay areas face considerable threats from these acid environmental attacks. This study focused on employing a "one-part" geopolymer (OPG) comprising ground granulated blast furnace slag (GGBFS), fly ash (FA), and solid sodium hydroxide (NH) to stabilize the soft clay. Simultaneously, the deterioration behavior of OPG stabilized soft clay under two different acids (HNO3 and H2SO4) with various pH values (pH of 2, 4, and 6) and varied immersion periods up to 240 days was evaluated including the mass loss, neutralization depth (ND), pH value, and unconfined compressive strength (UCS). Additionally, scanning electron microscopy (SEM) and X-ray energy spectrometry (EDS) characterized the evolution of microstructure and hydrate composition of OPGstabilized soft clay post varied acid immersion. The results highlighted the superior acid resistance of the stabilized soft clay with an 80:20 GGBFS/FA ratio compared to other ratios. The presence of significant hydration products, such as calcium silicate hydrates (C-S-H), calcium aluminate (aluminosilicate) hydrates (C-A-(S)-H), and sodium aluminosilicate hydrates (N-A-S-H), was observed in the OPG stabilized soft clay. In addition, the contents of Si in the OPG played a significant role in enhancing the acid resistance of the OPG stabilized soft clay. Based on these experimental results, two proposed mechanisms detailed the deterioration and acid resistance of the OPG stabilized soft clay under HNO3 and H2SO4 attack. The findings of this study contribute to advancing scientific comprehension concerning the acid resistance of the OPG stabilized soft clay in ground improvement practices.

Keyword ：

Ground granulated blast furnace slag and fly 'One-part " geopolymer Acid resistance ash Soft clay stabilization

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Abstract ：

An artificial alternative material for natural sand in construction is of significance for the civil engineering. In the present study, the effects of artificial geopolymer sand (AGS) as an alternative to natural sand (NS) on pore structure and mechanical property of cement mortar were studied. First, six groups of cement mortar specimens were prepared with the different replacement ratios (0.0%, 20.0%, 40.0%, 60.0%, 80.0% and 100.0%). Then, a series of nuclear magnetic resonance (NMR) tests were performed to study the effects of replacement ratio on the density, total porosity and percentage of different size pores. Finally, the ultrasonic wave and uniaxial compressive tests were performed to study the effects of replacement ratio on the P-wave velocity, strength and elastic modulus. The results show that the density and P-wave velocity decrease linearly as the replacement ratio increases. The total porosity increases slowly at first and then increases rapidly as the replacement ratio in-creases. The increase in replacement ratio induces the more significant increase in the smaller pores compared with the larger pores. The strength and elastic modulus firstly increase and then decrease as the replacement ratio increases. The strength and elastic modulus decreased by 11.0% and 5.4% when replacement ratio reaches 100%.

Keyword ：

Geopolymer Pore structure Mortar Mechanical property Artificial sand

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The use of solid waste and low-cost gel materials to replace or reduce the use of ordinary Portl and cement (OPC) in emulsified asphalt (EA) binder has positive significance for the comprehensive energy consumption and economic cost of cold mix asphalt (CMA) pavement. The proposed study investigates the interaction, rheological and physicochemical properties of emulsified asphalt (EA) with direct coal liquefaction residue based geo-polymers (DG) by fluorescence microscopy tests, the pH test, asphalt conventional tests, dynamic shear rheo-logical test (DSR), and Fourier transform infrared spectroscopy test (FTIR). The test results show that the reaction between DG mortar and EA particles was faster and more violent than that of OPC mortar, resulting in faster demulsification of EA. The added DG mortar increased the pH of the EA binder. Similar to OPC, DG decreased the penetration and ductility of EA evaporation residues, but increased its softening point. The addition of DG to EA changed the rheological properties of its evaporation residue, including complex modulus (G*) and phase angle (delta). Temperature sweep and frequency sweep test results show that DG was comparable to OPC in efficacy against EA residues, improving rutting resistance at the expense of fatigue performance. Complex modulus co-efficient (Delta G*) and complex viscosity coefficient (Delta eta*) indicate that the interaction of EA-DG is stronger than that of EA-OPC. FTIR analysis showed that the interaction between DG and EA is linked as a chemical bond.

Keyword ：

Geopolymer Emulsified asphalt Demulsification Direct coal liquefaction residue Interaction Rheological properties

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