Compressive Strength Loss Research Articles

Performance and deterioration mechanism of concrete incorporated with corrosion-inhibiting admixtures under the coupling effect of composite salt and freeze-thaw cycles

The purpose of this study is to provide multi-functional, green, low-carbon and environmental-friendly corrosion-inhibiting admixtures (CIA) to alleviate the deterioration of reinforced concrete under the coupling effect of composite salt and freeze-thaw cycles (FTCs). The effects of different contents of CIA on the performance of C30 concrete, including mechanical behavior (mass loss rate (MLR), compressive strength loss rate (CSLR) and relative dynamic elastic modulus (RDEM)), chloride ion penetration of concrete, and the electrochemical performance of rebars in concrete, were investigated. Furthermore, the deterioration mechanism of reinforced concrete was probed in detail by evaluating the pore structure parameters of concrete and the microscopic morphology of concrete and rebars via low-field nuclear magnetic resonance (NMR) and scanning electron microscope (SEM), respectively. The results showed that the mechanical behavior of concrete with CIA was prominently superior to that of concrete without CIA, with MLR decreased by 51.13–78.60%, CSLR decreased by 40.11–84.93%, and RDEM increased by 29.89–56.27% after 100 FTCs. The average content of free chloride ion in the concrete containing CIA was decreased by 12.14–55.65% under 100 FTCs due to the addition of CIA reducing the transmission path and the percentage of much detrimental pores (decreased by 39.03–85.99% after 100 FTCs). The correlation between free chloride ion content and diffusion depth conformed to Fick's second law, showing that there was a linear positive correlation between chloride diffusion coefficient (D) and FTCs. In addition, the electrochemical performance of rebars in concrete with CIA was improved owing to the good protection of CIA to rebars. This study is of great significance for improving the durability of reinforced concrete in harsh environment.

Effect of hydroxypropyl methyl cellulose (HPMC) as foam stabilizer on the workability and pore structure of iron tailings sand autoclaved aerated concrete

The stock of iron tailings sand (ITS) is massive and increases annually, posing a severe threat to the environment and necessitating proper disposal. This study aims to solve the problems of mesoscopic pore coalescence and disproportionation caused by excessive ITS in the production of autoclaved aerated concrete (AAC). The effects of the water-to-solid ratio (W/S) and foam stabilizer content on the performance of ITS autoclaved aerated concrete (ITS-AAC) were assessed. Furthermore, the mesoscopic and microscopic pore structures of ITS-AAC were investigated using optical methods and mercury intrusion porosimetry, respectively. The hydration and microstructure of the selected ITS-AAC samples were also analyzed using X-ray diffraction and scanning electron microscopy. The results show that under the same fluidity, the incorporation of 0.3%-0.6% hydroxypropyl methyl cellulose (HPMC) can significantly increase the gas-retaining performance of the slurry. A finer and more homogeneous pore structure was achieved by incorporating 0.6% HPMC, resulting in a smaller bulk density (23.1% decrease) and thermal conductivity (34.3% decrease) at the expense of a slight loss of compressive strength (13.8% decrease). This study provides a basis for adjusting the physical-mechanical properties of AAC by using foam stabilizers.

Bond performance between recycled concrete and steel bar after high temperature

Abstract To investigate the influence of high temperatures on the bond performance of recycled concrete and steel bar, this article considers the influence of different concrete types (ordinary concrete and recycled concrete) and different temperatures (20, 100, 150, 200, 250, and 300°C) on the concrete compressive strength and the bond performance of concrete and steel bar. On this basis, the calculation formula of bond strength and bond slip between concrete and steel bar after the high temperature is established. The test results show that the concrete compressive strength presents a downward trend with the increase in temperature; the compressive strength loss of recycled concrete is higher than that of ordinary concrete; when the temperature reached 300°C, the compressive strength loss of ordinary concrete is 24.4%, while that of recycled concrete is 41.6%. The bond strength of pull-out specimens decreases with the increase of temperature, while the bond slip increases with the increase of temperature; the bond strength between recycled concrete and steel bar is lower than that between ordinary concrete and steel bar, while the bond slip between recycled concrete and steel bar is higher than that between ordinary concrete and steel bar. This article can provide a theoretical basis for the application of recycled concrete in high-temperature environment.

Experimental study on the initial damage and mechanical property evolution of recycled coarse aggregates under freeze–thaw cycles and repeated loads

The natural aggregate fraction in recycled coarse aggregate (RCA) can yield initial damage during service and repeated crushing, which might affect the performance of recycled aggregate concrete (RAC). Therefore, in this study, freeze–thaw cycles and repeated loads of limestone were used to simulate the freeze–thaw cycles and load-induced damage of natural aggregates in RCA during service and repeated crushing. The properties of natural aggregates with initial damage were investigated to explore the mechanism of initial damage evolution and property degradation for natural aggregates in RCA. The results revealed that the compressive strength and tensile strength of RCA both decreased with the increasing number of freeze–thaw cycles or repeated loads. Furthermore, the interior damage for limestone under freeze–thaw cyclic loading was dominated by frost cracking, and the exterior damage was dominated by macroscopic cracking. However, when under repeated loads, the internal damage of limestone was dominated by macropores and fine pores, and the external damage pattern was dominated by interlayer cracks and intergranular tensile cracks. Additionally, both tensile strengths and elastic moduli decreased linearly with the increasing number of freeze–thaw cycles, while the loss of compressive strength was quadratically related to the number of freeze–thaw cycles.

Study of Some Durability Properties of Self-compacting Concrete Containing Waste Polyethylene Terephthalate

This study aims to investigate the durability properties and microstructural changes of self-compacting concrete (SCC) incorporating waste polyethylene terephthalate (PET) as fibers and as fine aggregate replacement. This is after exposed to saline environment (Alkalies, Sulphates, and Chlorides). PET effect into two forms was also evaluated for routine rheological properties of SCC and mechanical strength before and after exposure to sulphate salt. Five proportions of each form of PET incorporation in SCC mixtures were utilized. The volume fractions considered for PET as fibers were (0.25, 0.5, 0.75, 1.0, and 1.25)% by volume, with aspect ratio of 28%, and (2, 4, 6, 8, and 10)% by volume for fine aggregate replacements. Results indicated that the inclusion of PET adversely affected fresh propertis especially high proportions of PET as fine aggregate. Alkali silica reaction (ASR) outcomes illustrated an enhancement in the mix containing PET fibers, while fine-PET mix was slightly enhanced. Magnesium sulphate reduced mass and compressive strength of all mixes in percentages ranging from (0.18-0.90) % for mass loss and from (0.47-55.13) % for compressive strength loss. Ultrasonic pulse velocity (UPV) and dynamic modulus of elasticity (Ed) increased due to the sulphate impact except for M0.5 and M10 which decreased in both tests. Chloride's theoretical and modelled results illustrated higher diffusion coefficients and lower surface chloride content of fiber-PET mixes as compared to fine-PET mixes. The predicted SCC cover depths for fiber-PET mixes were lower than those predicted for fine-PET mixes for 20 and 50 years of service life design.

Physicochemical and Mechanical Behavior of the One-Part Geopolymer Paste Exposed to Hydrochloric and Sulfuric Acids

This paper aims to assess the durability of one-part geopolymer (OPG) pastes exposed to acidic environments. Two different acids (HCl and H2SO4) with different pH values (pH of 2, 4, and 6) were used to simulate the acidic environment in the current study. Acid resistance of the OPG paste activated by sodium hydroxide [NaOH (NH)] and sodium metasilicate [Na2SiO3 (NS)], respectively, was assessed in terms of pH variation, mass change, visual appearance, deterioration depth, and compressive strength loss for varied immersion periods (∼120 days). The scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS) and mercury intrusion porosimetry (MIP) tests were employed to investigate the evolution of porosity, morphological change, and hydrate composition for the varied immersion times. The experimental results revealed that due to the formation of a dense structure, the NS-activated OPG paste had better resistance to the acid attack compared with the NH-activated paste. It was also found that the gypsum crystals formed in the sample immersed in H2SO4 solution could fill the open pores and adhere to the surface of the sample, which reduced the further acid attack to some extent. However, the expansion properties of gypsums would lead to a loss of mechanical performance at the later immersion period. Furthermore, higher porosity of the OPG paste developed as the pH value of the acid solution decreased, thereby inducing the loss of mass and compressive strength and the increase of deterioration depth. Finally, as the immersion age and acid concentration increased, decalcification in the sample tended to occur, which caused a greater loss of compressive strength and a higher porosity. The outcome of this study could provide guidance for the application of the novel material in acid soil layer improvements or acid-resistant geotechnical structures.

Effect of spent bleaching earth ash on sulphate attack resistance of concrete

One of the severe durability problems of concrete is sulphate attack. Sulphate attack can cause expansion of concrete due to the formation of gypsum and ettringite. Recently, spent bleaching earth ash (SBEA) is being used as a partial cement replacement in concrete. In this study, the effects of unground SBEA (USBEA) and ground SBEA (GSBEA) on sulphate attack resistance on concrete in terms of expansion of mortar bar and loss in compressive strength of concrete exposed to 5% sodium sulphate solution were determined. The SBEA was ground in a planetary grinding ball mill for 30 min to obtain a finer particle size. The expansion of mortar bars exposed to sulphate conditions containing USBEA and GSBEA was evaluated for 6 months according to ASTM C1012. Meanwhile, the compressive strength of concrete containing USBEA and GSBEA against sulphate attack was determined at 28 and 90 days. It was found that the expansion of mortar bars containing GSBEA was the lowest (0.01%) among the specimens. The strength deterioration factor of concrete containing GSBEA against sulphate attack was the lowest, with 1.31% at 90 days. The findings showed that ground SBEA could be used to enhance the sulphate attack resistance of concrete.

Experimental investigation on leaching behavior of ultra-high performance concrete submitted to a flow environment

Ultra-high performance concrete (UHPC) is a cementitious material with exceptional durability. Uncertain is, however, the leaching behavior of UHPC in a flow environment. To investigate the leaching behavior of UHPC under the influence of moving water, accelerated tests simulating various naturally flowing solution conditions were conducted. The effect of flow environment, steel fiber content, and superplasticizer content on the degradation of UHPC was investigated. There are three flow velocities: static (0 m/s), low (0.3 m/s), and high (2 m/s), as well as three leaching solutions: 6 mol/L ammonium chloride, 3 mol/L ammonium chloride, and natural groundwater. Mass loss, porosity, degradation depth, flexural strength, and compressive strength were measured. The result showed that the maximum degradation of UHPC was observed in a high-velocity flow environment containing 6 mol/L ammonium chloride. Porosity, mass loss, degradation depth, and compressive strength loss following deterioration declined as the steel fiber content rose, reaching a minimum at 2% steel fiber in the same flow environment. The loss of flexural strength decreases and subsequently increases as the steel fiber content increases. The largest reduction in compressive strength was 16.4%, and the maximum reduction in flexural strength was 48.2%. At the same degraded ratio, the compressive strength loss of UHPC is significantly less than that of ordinary concrete. A predicted model for the loss of UHPC's cubic compressive strength is established.

Corrosion damage and life prediction of concrete structure in the coking ammonium sulfate workshop of iron and steel industry

Iron and steel plants emit a large amount of CO2 and SO2 in the production process, and the high concentrations of acid gases lead to serious corrosion damage of concrete structures. In this paper, the environmental characteristics and corrosion damage degree of concrete in a 7-year-old coking ammonium sulfate workshop were investigated, and the neutralization life prediction of the concrete structure was carried out. Besides, the corrosion products were analyzed through concrete neutralization simulation test. The average temperature and relative humidity in the workshop were 34.7 °C and 43.4%, and they were 1.40 times higher and 1.70 times less than those of the general atmospheric environment, respectively. Both the concentrations of CO2 and SO2 were significantly different in various sections of the workshop, and they were much higher than those of the general atmospheric environment. The appearance corrosion and compressive strength loss of concrete were more serious in the sections with high SO2 concentration, such as vulcanization bed section and crystallization tank section. The neutralization depth of concrete in the crystallization tank section was the largest, with an average value of 19.86 mm. The corrosion products gypsum and CaCO3 were obviously visible in the surface layer of concrete, while only CaCO3 could be observed at 5 mm. The prediction model of concrete neutralization depth was established, and the remaining neutralization service life in the warehouse, synthesis section (indoor), synthesis section (outdoor), vulcanization bed section, and crystallization tank section were 69.21 a, 52.01 a, 88.56 a, 29.62 a, and 7.84 a, respectively.

Carbon nanotube polymer nanocomposites coated aggregate enabled highly conductive concrete for structural health monitoring

Recently, we proposed a new strategy to develop a three-dimensional conductive network within a cement mortar by coating sand with graphene. In such a design, the interfacial transition zone (ITZ) was directly embedded in the conductive network, thus resulting in high piezoresistive performance. Considering that the ITZ between coarse aggregate and paste is typically much more vulnerable than that of the ITZ between fine aggregate and paste, here we extend this strategy to concrete, whose piezoresistive property has been rarely reported yet intimately relevant for practical application. Conductive fine and coarse aggregates are readily prepared by dipping coating with carbon nanotube (CNT) polymer slurry. Because of the high volume percentage of aggregates (∼70%) in concrete, the obtained concrete exhibit very high conductivity at low CNT usage of 0.41% (by weight of cement), several orders of magnitude higher than that reported before at similar CNT load. We find that the mixture incorporating conductive aggregates has a 28-day electrical resistivity of 1076 Ω cm with a compressive strength loss of 17.8%. On this basis, we further optimize the high-conductivity concrete by connecting conductive aggregates with a small amount of 0.25 wt% carbon fibre, which demonstrates an outstanding 28-day electrical resistivity of 235 Ω cm and an excellent fractional change in resistivity of ∼80%, more than one order of magnitude higher than those obtained in comparable systems. The experimental results also testify that our smart concrete exhibits acceptable mechanical properties and durability. The simple operation and low-cost benefits make our smart concrete demonstrate great potential for large-scale practical application.

Investigating the compressive strength and microstructural analysis of mortar containing synthesized graphene and natural pozzolan in the face of alkali-silica reactions

The high cost and agglomeration phenomenon of nano-graphene in cement matrix are considered major obstacles to applying graphene in the concrete industry. This research resolves both mentioned issues using synthesized graphene from graphite and surfactant by exfoliation method. On the other hand, the behavior of this material in Alkali–silica reaction (ASR) conditions is still unknown. Therefore, the main objective of this research is to investigate the performance of mortar by incorporating synthesized surfactant-based graphene and two natural pozzolans, pumice and zeolite, to mitigate ASR. First, the compressive strength of the studied mortars was measured in this study. Then, the behavior of the mixtures for 91 days in ASR conditions was assessed by measuring expansion, compressive strength loss, and various microstructure analyses. The results showed that the compressive strength of mortar containing 5 g/l of graphite and 0.56 g/l surfactant increased by 85.62% after 3 days of maturation compared with the surfactant-based mixture without graphite. The amount of expansion reduction in the graphene-based mixture with 15% replacement of cement by pumice after 28 and 91 days in ASR conditions is 215% and 194.2%, respectively, compared with the control mixture. In addition, the compressive strength loss of this mixture was negligible. The microstructure analysis showed that using synthesized graphene in mortars could mitigate ASR by forming a dense boundary structure around aggregates, and reducing OH‾ ion penetration. Furthermore, mixing pumice in the graphene-containing mixture could mitigate the ASR gel by lowering calcium silicates hydrates (C–S–H) dissolution and reducing transformation from tobermorite to polymerized C–S–H phase.

The Influence of Assembly Unit of Fibers on the Mechanical and Long-Term Properties of Reactive Powder Concrete

The corrosion of concrete structures by chloride salt is very significant in coastal environments. In order to improve the durability of marine concrete structures, cement-based materials with high durability need to be developed. In this investigation, the influence of NaCl freeze–thaw cycles (FT-C) and NaCl dry-wet alternations (DW-A) on the flexural and compressive strengths of reactive powder concrete (RPC) with an assembly unit of basalt fibers and steel fibers is studied. Additionally, the mass loss rate, the relative dynamic modulus of elasticity (RDEM), the chloride ion migration coefficient (CMC) and the impact toughness are measured after the NaCl FT-C and DW-A action. Our findings show that the RDEM, mass loss, and mechanical strength loss of RPC are increased by the ascending NaCl FT-C and DW-A. Meanwhile, the RDEM and the impact toughness are decreased by the NaCl FT-C and DW-A. The RPC with 0.5% basalt fibers and 1.5% steel fibers by volume of RPC shows the optimum mechanical performance and resistance to NaCl FT-C and DW-A. However, RPC with 3% steel fibers shows the worst resistance to NaCl erosion. The maximum mass loss rates, RDEM, flexural strength loss rate, compressive strength loss rate, CMC and impact toughness of all specimens after 300 NaCl FT-C and 30 NaCl DW-A are 4.5%, 91.7%, 28.1%, 29.3%, 3.2 × 10−12 (m2/s) and 2471 J. Meanwhile, the corresponding minimum values are 1.62%, 83.2%, 20.4%, 15.7%, 1.1 × 10−12 (m2/s) and 625 J. The researching findings will provide an optimum mix ratio of RPC with an assembly unit of basalt fibers and steel fibers, which can be applied in the marine engineering environment.

A prediction method for abrasion loss rate of some Egyptian carbonate rocks due to cyclic salt crystallization weathering using physico-mechanical deterioration: insights from laboratory investigations

Salt crystallization is the most important weathering processes that causes problems for rocks used as building stones. Therefore, assessment of the physico-mechanical properties of stones against cyclic salt crystallization is a critical issue for rock engineering applications in salty environmental conditions especially prone to abrasion. This research aims at investigating the relationship between the degradation of various physico-mechanical properties including apparent porosity, point load index, unconfined compression strength and abrasion loss rate for rocks during salt weathering process. For showing rock weathering in the salt crystallization process, five kinds of carbonate rocks were sampled from different areas of Egypt and subject to cyclic salt crystallization, up to twenty cycles. The variation rates of their physico-mechanical characteristics and abrasion loss values were calculated after each five cycles of salt weathering. The results showed that the studied rocks are suitable for use as building and decorative stones in areas prone to crystallization of salts, but attention must be paid to rocks with high porosity and low strength characteristics such as El-Minia limestone specimens. It was also found that there are strong linear correlations between the physico-mechanical degradation parameters and the abrasion loss rate of the studied rock samples at the end of the twentieth cycle of salt weathering. These relationships may be used to estimate the abrasion loss rate of the studied rock types against the cyclic salt weathering conditions and hence to make a rapid evaluation of the stone durability.

Hydration and phase conversion of MgO-modified calcium aluminate cement

This study evaluated the hydration and phase conversion of MgO-modified calcium aluminate cement (CAC). MgO was used to replace CAC at various dosages (0, 5, 10, 15, and 20 wt%) and the samples were exposed to a 60 °C atmosphere to expedite the conversion of the hydration products in CAC after curing initially at 20 °C. Microstructural analysis was carried out before and after expedited curing using various characterization techniques. During the initial curing, MgO can suppress the phase conversion, hindering the formation of stable phases (i.e., C3AH6 and AH3). After 28 days of expedited curing, a phase conversion can occur, with metastable phases converted to stable phases, due to which a strength reduction can be observed in all samples. Nevertheless, the development of hydrotalcite in samples modified with MgO could lessen the degree of the compressive strength loss. The addition of MgO can maintain the structural integrity before exposure by suppressing the conversion of metastable hydrates and after exposure through the formation of an Mg-Al LDH tetrahedral Al network as a secondary hydration product, maintaining the strength after exposure.

Freeze-thaw failure characteristics and strength loss of non-penetrating fractured rock mass with different fracture densities

Rock mass usually contains cracks, joints and other defects with different density and spatial combination characteristics in the diagenetic process. Under the freeze–thaw effect, they continue to expand and connect, which continuously weakens the strength property and poses a serious threat to the stability of rock mass. Previous studies paid more attentions to the strength reduction of rock, failing to directly reflecting the freeze–thaw damage characteristics of rock mass. In this paper, the freeze–thaw failure characteristics and strength loss of non-penetrating fractured rock mass with different fracture densities were studied by means of theoretical derivation and laboratory tests. Firstly, non-penetrating fractured rock mass samples with different fracture conditions were prepared. Then the freeze–thaw samples were subjected to laboratory compression tests and the loss of uniaxial compressive strength was measured. On this basis, the theoretical values of geological strength index GSI was calculated for the samples, and the rough prediction empirical model of GSI for non-penetrating fractured rock mass treated with different freeze–thaw cycles was obtained through data fitting. Finally, by combining the apparent observation method with acoustic emission monitoring technique, the effects of freeze–thaw cycles and fracture density on the failure characteristics of non-penetrating fractured rock mass samples were analyzed comprehensively from both the macro and micro perspectives.

Experimental assessment of mechanical and physical performance of latex modified concrete with fine recycled aggregate

One of the most crucial building materials is concrete. However, producing concrete consumes a significant amount of natural resources. Attention has been focused on using concrete debris and recycling it in the building industry to solve this issue. This study investigates latex-modified concrete's physical and mechanical performance when replacing fine natural aggregates (FNA) with different percentages of fine recycled aggregates (FRA). The study includes conducting laboratory tests to investigate the workability, slump loss, compaction factor, compressive strength, ultrasound pulse velocity, absorption, and porosity. When replacing fine natural aggregates (FNA) with different percentages of fine recycled aggregates (FRA), it was found that there is an inverse relationship between the slump, compressive strength, compaction factor, and the percentage of RFA. The existence of SBR latex in concrete to form polymer modified concrete led to a higher decrease in workability compared to unmodified concrete. The absorbability increases as the proportion of fine natural aggregates are replaced by recycled fine aggregates, possibly due to the higher porosity of recycled fine aggregates. The same conclusion can be generalized to the results of the porosity test. However, adding the polymer improves the absorption resistance and reduces the porosity when replacing the fine natural aggregate with the fine recycled aggregate. Additionally, the outcomes demonstrated that SBR latex compensates for the compressive strength loss caused by recycled fine aggregates.

Addition of Phosphogypsum to Fire-Resistant Plaster Panels: A Physic–Mechanical Investigation

Gypsum (GPS) has great potential for structural fire protection and is increasingly used in construction due to its high-water retention and purity. However, many researchers aim to improve its physical and mechanical properties by adding other organic or inorganic materials such as fibers, recycled GPS, and waste residues. This study used a novel method to add non-natural GPS from factory waste (phosphogypsum (PG)) as a secondary material for GPS. This paper proposes to mix these two materials to properly study the effect of PG on the physico-mechanical properties and fire performance of two Tunisian GPSs (GPS1 and GPS2). PG initially replaced GPS at 10, 20, 30, 40, and 50% weight percentage (mixing plan A). The PGs were then washed with distilled water several times. Two more mixing plans were run when the pH of the PG was equal to 2.4 (mixing plan B), and the pH was equal to 5 (mixing plan C). Finally, a comparative study was conducted on the compressive strength, flexural strength, density, water retention, and mass loss levels after 90 days of drying, before/after incineration of samples at 15, 30, 45, and 60 min. The results show that the mixture of GPS1 and 30% PG (mixing plan B) obtained the highest compressive strength (41.31%) and flexural strength (35.03%) compared to the reference sample. The addition of 10% PG to GPS1 (mixing plan A) improved fire resistance (33.33%) and the mass loss (17.10%) of the samples exposed to flame for 60 min compared to GPS2. Therefore, PG can be considered an excellent insulating material, which can increase physico-mechanical properties and fire resistance time of plaster under certain conditions.

Study on Mechanical Properties and Action Mechanism of Leather Industrial Sludge Aggregate Baking-Free Bricks

Taking an industrial sludge and its preparation of sludge wrap shell aggregates (WSAs) instead of sand to prepare baking-free brick as the research object, the development law of mechanical properties and the influence mechanism of macro and micro characteristic parameters of the bricks under different sludge and WSAs replacement rates were studied through the macroscopic mechanical properties test, with the help of nuclear magnetic resonance (NMR), transmission electron microscopy-energy spectrum and other testing technology and pores and cracks analysis system (PCAS) software. The results showed that the compressive strength of each sample decreased with the increase of sludge content. When the sludge content was less than 30%, it was mainly affected by the water-binder ratio. When the sludge content was more than 30%, it was mainly affected by the sludge content. At the age of 7 days, with the increase in replacement rate of WSAs, the compressive strength of the S10 and S30 groups was higher than that of the control group. The compressive strength of the S50 experimental group was 30.38 MPa, and the loss of compressive strength was slight compared with the control group. The water absorption rate of the 28 days S100 experimental group increased by 10.71% compared with the control group. When the content of WSAs was less than 50%, the holes above 0.1 μm in the brick can be reduced and transformed into smaller holes, with a decreasing trend of the plane porosity of the brick. The microscopic results of the baking-free brick showed that the three-phase system of WSAs-interface transition area-mortar was poorly bonded and delaminated compared with the gravel aggregate-interface transition area-mortar system, and damage was more likely to occur in the WSAs and interface transition area. The above results show that it is feasible to use sludge and WSAs instead of sand for the preparation of baking-free bricks. This technology not only solves the problem of sludge disposal, but also protects the over-exploitation of mineral resources, and the technology has a broad application prospect and market value.

Corrosion of ordinary Portland cement and metakaolin-based geopolymer immersed in nitric acid solution

Preventing the corrosion of cementitious materials in acidic environments is crucial for the safety and durability of infrastructure. The corrosion of specimens of ordinary Portland cement (OPC) and metakaolin-based geopolymer (MKG) in 1 mol/l nitric acid solution was investigated in this work. The changes in morphology, mass, compressive strength, pH, chemical composition, crystal phases and pores were compared and analysed. The surfaces of the OPC specimens were corroded into petaloid grooves due to the relatively severe reaction between the calcium hydrated products and the nitric acid solution. The increase in the porosity of the OPC specimens was greater than that of MKG specimens, whose main constituents reacted with the nitric acid solution relatively mildly. However, large quantities of fragments peeled away from the MKG specimens, and their mass and compressive strength losses were greater than those of the OPC specimens. The porosities of the MKG specimens were only slightly changed. The strength loss of the MKG specimens was mainly due to broken matrix structures and newly formed porous silicious frameworks.

Gray correlation analysis of factors influencing compressive strength and durability of nano-SiO2and PVA fiber reinforced geopolymer mortar

AbstractTo investigate the mechanical properties and durability of nano-SiO2, polyvinyl alcohol (PVA) fiber-modified fly ash (FA), and metakaolin (MK)-based geopolymer mortar (FMGM), tests of compressive strength, electrical flux, freeze–thaw cycles, and sulfate dry and wet cycles were conducted. Based on the experimental results, combined with Dunn’s gray correlation theory analysis method, a mathematical analysis of the effect sensitivity of the contents of the four mixtures on the mechanical properties and durability of FMGM was carried out. The method of gray correlation analysis can solve the mathematical problem with partial unclear and uncertain information, and the method requires less data and less computation compared with other mathematical analysis method. The results showed that the gray correlation degree between the content of MK and the electric flux value is higher than the that of other comparison sequence and each reference sequence, while the gray correlation degree between the PVA fiber dosage and the loss rate of compressive strength is lower than that of other comparison sequence and each reference sequence. The influence of the four mixture contents on the compressive strength and mass loss rate was in the following decreasing order: MK and FA, PVA fiber, and nano-SiO2. In addition, the influence of the four material mixture contents on the electric flux value and compressive strength loss rate was consistent in the following decreasing order: MK and FA, nano-SiO2, and PVA fiber. Furthermore, the mechanical properties and durability reached the optimum when the PVA fiber content was 0.6% and the dosage of nano-SiO2was 1.0%. The results of this study can provide a new method for the analysis and evaluation of mechanical properties and durability of nano-SiO2and PVA fiber-reinforced FMGM in future.