Mechanism Of Strength Development Research Articles

Experimental Study on The Mechanism of Strength Development and The Durability of Chemical Injection Improved Body

Experimental Study on The Mechanism of Strength Development and The Durability of Chemical Injection Improved Body

A novel high-performance warm-mix porous asphalt prepared with polyurethane prepolymer: Strength development mechanism and mechanical and functional performance

The relatively poor durability of porous asphalt (PA) is one of the major concerns that limit its wider application. One common approach to enhance the durability of PA is to use high-viscosity polymer-modified asphalt binder. However, this method can result in increased construction temperature, thus raising various associated environmental concerns. The aim of this study is to explore the potential of using polyurethane prepolymer modified porous asphalt (PUPA) as a novel high-performance PA with relatively low construction temperature. The optimum polyurethane prepolymer (PUP) content and compaction temperature of PUPA were first determined through the Marshall test and compaction energy index (CEI). Then, the strength development of PUPA was characterized by the indirect tensile stiffness modulus (ITSM) test. The engineering performance of PUPA was evaluated by means of the Cantabro abrasion test, indirect tensile fatigue (ITF) test, wheel tracking test, and freeze-thaw splitting test. The results showed that the optimum PUP content was 10%, and the compaction temperature of the PUPA can be as low as 130 °C. The curing reactions between PUP, aggregate and airborne moisture was found to contribute to the strength enhancement of PUPA. Moreover, the overall performance of PA can be significantly improved with the incorporation of PUP. This study proved the high potential of building low-carbon durable PA pavement with PUPA.

Elemental Design of Alkali-Activated Materials with Solid Wastes Using Machine Learning.

Understanding the strength development of alkali-activated materials (AAMs) with fly ash (FA) and granulated blast furnace slag (GBFS) is crucial for designing high-performance AAMs. This study investigates the strength development mechanism of AAMs using machine learning. A total of 616 uniaxial compressive strength (UCS) data points from FA-GBFS-based AAM mixtures were collected from published literature to train four tree-based machine learning models. Among these models, Gradient Boosting Regression (GBR) demonstrated the highest prediction accuracy, with a correlation coefficient (R-value) of 0.970 and a root mean square error (RMSE) of 4.110 MPa on the test dataset. The SHapley Additive exPlanations (SHAP) analysis revealed that water content is the most influential variable in strength development, followed by curing periods. The study recommends a calcium-to-silicon ratio of around 1.3, a sodium-to-aluminum ratio slightly below 1, and a silicon-to-aluminum ratio slightly above 3 for optimal AAM performance. The proposed design model was validated through laboratory experiments with FA-GBFS-based AAM mixtures, confirming the model's reliability. This research provides novel insights into the strength development mechanism of AAMs and offers a practical guide for elemental design, potentially leading to more sustainable construction materials.

Microstructure, strength development mechanism, and CO2 emission analyses of alkali-activated fly ash-slag mortars

A comprehensive investigation was conducted to examine the influence of fly ash/slag mass ratio on the strength and microstructure of alkali-activated fly ash-slag (AAFS) mortars. NaOH and Na2SiO3 were employed as activators for different fly ash/slag ratios. The results revealed that AAFS mortar with a fly ash/slag ratio of 25/75 exhibited the highest strength, reaching 104 MPa. The porosity and gel content of AAFS showed a weak correlation with compressive strength, emphasizing the significant impact of the generated gel type on AAFS strength. The comprehensive evaluation of AAFS strength incorporates factors related to the structure and chemical composition of reaction products. A strength index derived from AAFS mortar is proposed and validated against seven additional literature datasets from different systems, demonstrating a robust correlation between the calculated index and the compressive strength. Furthermore, carbon emission analysis reveals that, compared to OPC, FA100 exhibits 7.9%–21.2% lower carbon emissions, while FA25BF75 shows 0.1%–97.5% lower CO2 intensity than OPC, owing to the higher strength of AAFS. In general, AAFS exhibits improved properties and environmental benefits, indicating significant potential for practical applications as a complete replacement for OPC.

Utilization of ground granulated blast-furnace slag and electrolytic manganese residue as a low-carbon cementitious material

Ground granulated blast-furnace slag (GGBS) is a common substitute for ordinary Portland cement (OPC). However, GGBS–OPC lacks early strength when OPC content is low (<50%). A new cementitious material called GGBS–OPC–EMR (GOE) was developed by adding electrolytic manganese residue (EMR) to address this issue. Tests were conducted using XRD, SEM, and TG to analyze the micro-structural mechanisms of strength development in GOE. Environmental and economic evaluations were conducted, including CO2-eq (carbon dioxide equivalent) analysis, leaching tests, and economic analysis. Results showed that mixture of GGBS, OPC, and EMR in a 4:2:1 ratio increased the unconfined compressive strength by 25% after 28 days compared to OPC while reducing cement consumption by 70%. Major hydration products in GOE were C–S–H and ettringite (AFt), with approximately 14% EMR promoting AFt production. GOE reduced CO2-eq emissions by 35.9% and saved $46.6/ton compared to OPC. Leaching tests demonstrated GOE's ability to stabilize heavy metals, sulfate, and ammonia nitrogen.

Strength Assessment of Water-Glass Sand Mixtures.

For years, the chemical injection process has aided construction works by increasing the strength and water-sealing efficiency of sandy soil. Despite its growing popularity in projects, such as seismic strengthening and liquefaction mitigation, a unified understanding of how chemically treated soil develops its strength, especially under static conditions, remains elusive. Some studies have proposed that strength is derived from the tensile effects of dilatancy, where shearing of the sandy soil causes expansion, creating tension in the interstitial hydrogel and resulting in negative pressure that consolidates the soil particles. Other studies, however, attribute this strength development to the volumetric shrinkage of the hydrogel, which the authors argue confines and compresses the sandy soil particles. Challenges are encountered with this theory, particularly with respect to the consistency of the volumetric shrinkage measurements and the timing of these measurements in relation to changes in soil strength. The aim of the current research is to shed light on this mechanism by using consolidation drainage triaxial compression (CD) tests to measure the cohesive strength and internal friction angle of chemically enhanced soil. By eliminating the dilatancy-induced negative pressure effects and coupling this with an analysis of the molecular structure of the hydrogel, the present study provides an in-depth look at the strength development mechanism and its durability. This holistic approach not only fills in the existing gaps in the understanding of this mechanism, but also paves the way for optimized construction techniques.

Geopolymer-stabilized soils: influencing factors, strength development mechanism and sustainability

This paper presents the strength and micro-structural characteristics of high plasticity expansive clay stabilized with ordinary Portland cement (OPC) and geopolymers. Furthermore, sustainability aspects such as cost-efficiency, energy consumption and eco-efficiency of the OPC and geopolymer-stabilized soils were compared. The experimental results revealed that the geopolymer-stabilized soils exhibit higher strength and sustainability performance than the OPC-stabilized soils. This study also explores the developed machine learning prediction models of the geopolymer soils’ unconfined compressive strength (UCS) based on experimental data from current research and previous literature. Linear regression (LR), K-nearest neighbour (KNN), random forest (RF), random forest with random search hyperparameter optimization (BRRF) and random forest with grid search hyperparameter optimization (BGRF) were used as part of ensemble algorithms to predict stabilized soils UCS. Eight parameters such as liquid limit (LL), plasticity index (PI), ground granulated blast furnace slag (S) content, fly ash (FA) content, the molarity of NaOH (M), activator to binder ratio (A/B), Na/Al and Si/Al were used as input to predict UCS of geopolymer soils. The following metrics were used to assess the models’ predictive ability for compressive strength: coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE) and mean square error (MSE). The BRRF model has a good potential to predict the UCS of geopolymer soils, according to the findings of its testing (MAE = 0.27, MSE = 0.21, RMSE = 0.46, R2 = 0.99) and training (MAE = 0.78, MSE = 1.48, RMSE = 1.23, R2 = 0.96) phases. According to the RF model's feature importance study, slag content and liquid limit were found to influence forecasting compressive strength, while fly ash content has the least influence.

Research on microscopic contact characteristics of aggregates during compaction of asphalt mixtures

The compaction process is the stage when the skeleton structure and strength of asphalt mixture are developed. In order to explore the strength development mechanism of asphalt mixture skeleton, the microscopic contact characteristics of aggregates during asphalt mixture compaction process were evaluated. Firstly, the CT scanning and image processing techniques were employed to obtain digital images of the asphalt mixture during the compaction process. Then, the processed digital images were reconstructed in three dimensions to achieve dynamic simulation of the asphalt mixture compaction process. A novel index of contact chains was proposed to characterize the different state of aggregate contact within the asphalt mixture, and then, the characteristic parameters of contact chains during compaction, such as the number of contact chains, contact chain length, and contact chain angle, were analyzed. The results showed that for the typical used SMA-13 asphalt mixture, the primary role of 13.2–16 mm grade aggregates in the asphalt mixture was to form the main skeletal structure, and 4.75–9.5 mm and 9.5–13.2 mm grade aggregates provided more than 90% of the contact points for the asphalt mixture. The contact chains formed by the aggregates of 4.75–9.5 mm and 9.5–13.2 mm were the main source of strength of the asphalt mixture. The aggregate was dominated by migrating movements in the early and middle stages of compaction, and rotating movements in the later stages of compaction dominated the aggregate.

Influence of bagasse ash powder and marble powder on strength and microstructure characteristics of alkali activated slag concrete cured at room temperature for rigid pavement application

In this research, an attempt is made to partially replace ground granulated blast furnace Slag (GGBS) with a binder rich in SiO2 and CaO in alkali activated slag concrete (AASC) to increase workability and setting time. GGBS is replaced with bagasse ash powder (BAP) in 5%, 10%, and 15% of the binary mix, and subsequently with marble powder (MP) in 5% and 10% of the binary mix. After establishing the best mix for both binder replacements, a ternary mix with 5% BAP and 10% MP is created. The fine aggregates used in the comparison are 100 % river sand and slag sand. 10 M sodium hydroxide and the alkaline to binder ratio is 0.4, were used. Mechanical properties such as compressive strength, split tensile strength, and flexural strength are performed cured at 1, 3, 7, and 28 days samples. To further understand the intrinsic mechanism of strength development, microstructure, morphology and mineralogy on AASC are investigated. Based on the findings, it can be inferred that AASC mixes have a higher strength than OPC mixes. The mechanical strengths of the AASC binary mix with 10% MP and 5% BAP are higher. The microstructural analysis reveals the mixes developed with BAP and 100 % GGBS, had a denser microstructure than the normal mixes. The mechanical properties obtained for most of the AASC mixes are significantly higher than the IRC SP:62-2014 recommendations for rigid pavements for low volume roads.

Study on Strength Development Mechanism of Organic Soil in Dianchi Lake, China

The organic soil is widely distributed around Dianchi Lake in Kunming, which is rich in the humic group (HG). In order to explore the effect of HG on the strength development of organic soil, this paper adopts the method of adding humic acid (HA) reagent into the undisturbed cohesive soil (blending method) and soaking it in fulvic acid (FA) solution (steeping method) to simulate the organic soil. Then, the effect of HG on soil is analyzed by the unconfined compressive strength (UCS) and the scanning electron microscope (SEM) tests. The UCS test shows that HA can significantly reduce the UCS of the samples, and it continues to decrease with the increase of the HA reagent content. FA can substantially enhance the UCS of the samples, which continues to increase with the concentration of FA solution (decreasing the pH value). Under each HG condition, the steeping of FA can significantly increase the UCS of the sample when the content of the HA reagent is less than 10%, and the growth rate of the UCS decreases when it is greater than 10%. With the increase of steeping age, the UCS of the 5% HA samples continued to increase and gradually became stable, and when the content of the HA reagent is more than 5%, the UCS curve first increases and then decreases. The SEM test shows that adding HA reagent can significantly increase the pore size, improve the connectivity between the pores, and weaken the connection of the soil structure. The steeping of FA can reduce the pore size, weaken the connectivity between the pores, and strengthen the connection of the sample structure.

Strength development and microcosmic mechanism of waste glass powder cement mortar

In this article, the strength characteristics of the cement mortar with waste glass powder of different size and content at different ages were studied. The mechanism of strength development was analysed from the microstructure of mortar specimens based on scanning electron microscopy (SEM) and electronic dispersive spectroscopy (EDS). The results show that the compressive strength and flexural strength of the mortar specimens increase significantly with a higher age. There is an optimal content of glass powder corresponding to the maximum strength. The glass powder of smaller particle size clearly promotes the development of compressive strength and flexural strength in the mortar specimens. It is found from SEM-EDS that glass cement mortar has a larger amount of internal hydration products and higher density compared with ordinary cement mortar. The density of cement mortar incorporating 15 wt% glass powder increases gradually with the decrease of glass particle size. The hydration products and compactness of the cement mortar adding 200–500 mesh glass powder experience an increase and then a decrease with a rise in the glass content. The strength enhancement with the addition of glass powder are mainly attributed to the microaggregate filling effect and pozzolanic effect of the glass powder, as well as to changes in the interfacial transition zone.

Effect of Calcium Carbide Residue on Strength Development along with Mechanisms of Cement-Stabilized Dredged Sludge.

The purpose of this research is to explore the feasibility of using calcium carbide residue (CCR), a by-product from acetylene gas production, as a solid alkaline activator on the strength development in CCR–Portland cement-stabilized dredged sludge (CPDS). The effects of cement content, CCR content and curing time on the strength development of CPDS were investigated using a series of unconfined compressive strength (UCS), pH and electric conductivity (EC) tests. Scanning electron microscopy and X-ray diffraction analyses were performed to gain additional insight into the mechanism of strength development. Meanwhile, the carbon footprints of CPDS were calculated. Following the results, it was found that CCR can significantly improve the strength of cemented dredged sludge. On the basis of the strength difference (ΔUCS) and strength growth rate (UCSgr), it was recommended that utilizing 20% cement with the addition of 20% CCR is the most effective way to develop the long-term strength of CPDS. In addition, the microstructural analysis verified that the optimum proportion of CCR benefits the formation of hydration products in CPDS, particularly needle-like gel ettringite, resulting in a less-porous and dense inter-locked structure. Furthermore, the solidification mechanism of CPDS was discussed and revealed. Finally, it was confirmed that CCR can be a sustainable alternative and effective green alkaline activator for the aim of improving cemented dredged sludge.

Coupled effects of fly ash and calcium formate on strength development of cemented tailings backfill

Cemented tailings backfill (CTB) is widely adopted to ensure the safety of underground goafs and mitigate environmental risks. Fly ash (FA) and calcium formate (CF) are common industrial by-products that improve the mechanical performance of CTB. How the coupling of the two components affects the strength development is not yet well-understood. Neural network modelling was conducted to predict the strength development, including the static indicator of uniaxial compressive strength (UCS) and the dynamic indicator of ultrasonic pulse velocity (UPV). Sobol' sensitivity analysis was carried out to reveal the contributions of FA, CF and curing time to CTB strength. SEM microstructure investigation on CTB samples was implemented to reveal the mechanism of strength development and justify the predictions by neural network modelling and sensitivity analysis. Results show that the combination of FA content, CF content and curing time can be used to predict both UCS and UPV while providing adequate accuracy. The maximum of UCS of 6.1215MPa is achieved at (FA content, CF content, curing time) = (13.78 w%, 3.76 w%, 28days), and the maximum of UPV of 2.9887km/s is arrived at (FA content, CF content, curing time) = (11.67 w%, 3.08 w%, 10days). It is also implicated that prediction of UCS using UPV alone, although common in field application is not recommended. However, UPV measurement, in combination with the information of FA dosage, CF dosage and curing time, could be used to improve UCS prediction. The rank of variable significance for UCS is curing time > FA content > CF content, and for UPV is FA content > curing time > CF content; variable interaction is strongest for FA with CF for UCS development, and for FA with curing time for UPV evolution. Influence of FA on CTB strength development is due to improved polymerisation and consumption of Ca(OH)2. Influence of CF on strength development is a result of accelerated hydration and increased combined-water content in calcium silicate hydrate (CSH). Effect of curing time is attributed to the evolution of CSH product and pore-water content during cement hydration.

Black Cotton Soil Stabilization by Using Fly Ash - Kota Stone Slurry Mix

Abstract: The usage of waste material for stabilizing black cotton soil has been a sustainable interest. Kota stone slurry is a waste from kota stone and fly ash is a waste from industries containing high amount of sodium and magnesium, was used as a soil stabilizer for blac cotton soil improvement in this study. This research investigated the effects of sizes and percentages of kota stone slurry mix and fly ash on the physical and strength properties, which included particle size distribution, Atterberg limits, compaction, and unconfined compressive strength (UCS) of blac cotton soil. Micro structural characterization, including the scanning electron microscopic, energy dispersive X-ray spectroscopy, and X-ray diffraction was conducted on both untreated and treated black cotton soil samples to examine the mechanism of strength development. The addition of kota stone slurry and fly ash reduced the water holding capacity, which then caused the reduction in soil plasticity (from 18 to 11%) and optimum water content (from 20 to 16%) along with the increase in peak dry density (from 1.66 to 1.74 Mg/m3). The strength of black cotton soil may increased from 50 to almost 220 kPa. The optimum kota stone slurry and fly ash contents, providing the highest UCS, were at 20 and 30% for 0.063 mm kota stone slurry and fly ash and 0.15 mm kota stone slurry and fly ash, respectively. The UCS improvement of treated marine clay is attributed to the formation of cementation compounds, mainly aluminum magnesium silicate hydrate (A–M–S–H). The outcome of this research will allow the use of RBT as a low-carbon soil stabilizer across civil engineering applications. Keywords: Stablization, Fly ash, kota stone slurry, Atterberg limits, Compaction, and unconfined compressive strength

Strength development mechanism of a marine binding material with red mud and seawater

This experiment works on red mud, blast furnace slag, desulfurized gypsum, fly ash, and seawater as raw materials to make a marine binding material. It is found that using seawater as mixing water in red mud based binding materials can promote the strength development comparing to using freshwater. The optimal ratio of red mud, blast furnace slag, cement, desulfurized gypsum, fly ash and externally polycarboxylate superplasticizer is 30%, 19%, 40%, 6%, 5% and 1.5%, respectively. Under the seawater to binder ratio of 0.33, the compressive strength of mortar specimen can reach 36.34 MPa, and the flexural strength can reach 11.32 MPa on the 28th day. Microstructural characterization results indicate that under the double stimulation of alkalinity from red mud and compound salts from seawater, more and more active ions of silicon and aluminum are released to form C-A-S-H gel and ettringite during the hydration of marine binding material. The micro-aggregate filling effect of red mud and hydration acceleration provided by the compound salts in seawater can improve pore structure of the hardened marine binding material. The utilization of red mud in this work can fulfill the green concept of development and avoid potential risk of environment pollution.

The effect of leachate seepage on the mechanical properties and microstructure of solidified sludge when used as a landfill temporary cover material.

In this study, the effect of leachate seepage on the strength properties of a landfill temporary cover material: sewage sludge solidified with soda residue, ground granulated blast furnace slag, and quicklime, was investigated using small-scale column tests. The strength of the solidified sludge was reflected by penetration resistance with a micro penetrometer. The results showed that the penetration resistance increased at first, but then decreased with the increase in duration. The peak value for penetration resistance appeared at around the 75th day under the effect of leachate seepage. In contrast, without leachate seepage, penetration resistance increased at first as duration increased and then remained stable. The main hydration products were calcium silicate hydrate, ettringite and hydrocalumite. Some pollutants, such as copper, chromium, and arsenic, were also stabilized by the solidified sludge. The nuclear magnetic resonance results showed that the sample with highest penetration resistance had a reduced pore volume, especially macropore volume. Furthermore, leachate corrosion and the removal of some substances contributed to the decrease in penetration resistance after long-term seepage. The strength performance of temporary cover in laboratory short-term seepage and leachate soaking environments might be different from that in a landfill leachate seepage environment. This study improves understanding about the performance of temporary cover materials in landfill.

Positive Influence of Liquid Sodium Silicate on the Setting Time, Polymerization, and Strength Development Mechanism of MSWI Bottom Ash Alkali-Activated Mortars.

Setting time and mechanical properties are key metrics needed to assess the properties of municipal solid waste incineration (MSWI) bottom ash alkali-activated samples. This study investigated the solidification law, polymerization, and strength development mechanism in response to NaOH and liquid sodium silicate addition. Scanning electron microscopy and X-ray diffraction were used to identify the formation rules of polymerization products and the mechanism of the underlying polymerization reaction under different excitation conditions. The results identify a strongly alkaline environment as the key factor for the dissolution of active substances as well as for the formation of polymerization products. The self-condensation reaction of liquid sodium silicate in the supersaturated state (caused by the loss of free water) is the major reason for the rapid coagulation of alkali-activated samples. The combination of both NaOH and liquid sodium silicate achieves the optimal effect, because they play a compatible coupling role.

Uncovering the effect of fly ash cenospheres on the macroscopic properties and microstructure of ultra high-performance concrete (UHPC)

Fly ash cenosphere (FAC) is used as a supplementary cementitious material (SCM) to prepare ultra high-performance concrete (UHPC). The replacement of cement with FAC in UHPC is beneficial for the workability of fresh UHPC and from the perspective of mechanical and microstructure development. The influence of FAC with different dosages (0–40% of binders by volume) on the mechanism of strength development was investigated by mechanical, rheological and microstructural measurements. The results indicate that FAC shows a marginal enhancement of the hydration process of UHPC in the early hydration period and the predominant filler effect at 28 days. The additionally formed hydration products from the pozzolanic reaction of FAC contribute to gradually refining the pore structure and slowly increasing the compressive strength of UHPC. While the early-age compressive strength of the UHPC matrix with FAC is inadequate, the ‘ball-bearings’ and water-reducing effect of FAC particles obviously reduce the viscosity in the UHPC paste. FAC can work as an inorganic viscosity breaking agent to improve the flowability of UHPC for a variety of engineering applications.

Strength development and deterioration mechanisms of foamed asphalt cold recycled mixture based on MD simulation

The recycling and reuse of asphalt pavement have become requirements for environmental protection. Foamed asphalt cold-recycling technology is drawing extensive attention and being widely applied. Foamed asphalt cold recycled mixture has advantages such as energy savings, reduced asphalt content, and low transportation costs, and it has the characteristics of both rigid and flexible pavement. However, foamed asphalt mixtures are complex in composition, as it includes recycled asphalt pavement (RAP), water, new asphalt, aggregate, and cement. Therefore, the interaction mechanisms between recycled asphalt pavement and cement or foamed asphalt within the presence of water in the mixing, curing and service procedures will play a key role in determining the development and deterioration of strength of foamed asphalt cold recycled mixture, which was however not well clarified. This study firstly specified the decrease of strength of foamed asphalt cold recycled mixture when considering the effect of water in field project. It was found that the strength of foamed asphalt cold recycled mixture increased along with the decrease of water content during the curing procedure, and decreased by 15–20% through the winter frost. Then the interaction between RAP and cement or foamed asphalt within and without the presence of water had been analyzed with molecular simulation method. The mechanisms of strength development and deterioration of foamed asphalt cold recycled mixture were clarified from the point of view of molecular interaction. The simulation results indicate that the adhesion strength between RAP and cement is greater than that between RAP and new asphalt. The presence of water simultaneously weakens the adhesive bond strengths between RAP and cement and RAP and asphalt.

Preparation and characterization of the greener alkali-activated grouting materials based on multi-index optimization

As a green and carbon-friendly material, alkali-activated grouting material (AAGM) has great application potential in reinforcement engineering. In this study, the alkali-activated slag/fly ash grouting material (AASFGM) was prepared with industrial-waste ground granulated blast-furnace slag (GGBS) and fly ash (FA) as raw materials. In order to meet the multi-performance requirements, a multi-index optimization design based on grey correlation and objective weight was adopted to prepare AASFGM pastes. And its physical performances including fresh and harden properties were tested and compared with those of cement grouting materials (CGM), more than that, the microstructure and strength development mechanism of AASFGM was further characterized by means of X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Energy-dispersive Spectrum (EDS) and Fourier transform infrared spectroscopy (FT-IR). It is found that the AASFGM paste possesses clean production, high mechanical strength, high fluidity, low bleeding rate and low porosity, providing appealing properties as grouting materials for reinforcement. The new multi-index optimization method, based on grey correlation and objective weights determined, is much more scientific and objective to obtain a balanced performance for AASFGM preparation. The optimized AASFGM paste has a uniform and compact microstructure, and it also has remarkable advantages in mechanical strength, bleeding rate and porosity compared with CGM. As a carbon-friendly grouting material, it may become a greener substitute of CGM for the cleaner reinforcement engineering.