7-day Unconfined Compressive Strength Research Articles

Experimental Performance of Filling Material with Modified Red Mud for Roadbed

Cement-modified red mud as roadbed filler was investigated through tests, including compaction, California Bearing Ratio (CBR), modulus of resilience (E0), unconfined compressive strength (UCS), and scanning electron microscopy. Optimum moisture content (ω0), maximum dry density(), CBR, modulus of resilience, UCS, and microscopic characteristics of red mud were analyzed in different modified states. An optimal cement admixture for red mud modification was proposed. Results showed that (1) adding cement significantly improved CBR and modulus of resilience, (2) cement-modified red mud exhibited faster initial strength formation, with 7-day UCS over 65% of 28-day UCS, (3) water stability and frost resistance improved significantly with 4% and 6% cement dosing, (4) recommended cement admixture was 1.1% without adverse conditions, but not less than 6% with water immersion. Modified red mud is unsuitable for seasonal frozen regions. The recommended blending and leaching concentration met regulatory requirements, meeting technical, environmental, and economic goals for roadbed filler in highway construction.

Optimum Design of Mixture Proportion and Microscopic Analysis of Cement-Stabilized Macadam by Rubber Powder and Fiber

Abstract Based on the orthogonal test method, the mixture proportion design of cement-stabilized macadam (CSM) modified with rubber powder and fiber is studied. With strength and dry-shrinkage as key indices, the influence of length of polyvinyl alcohol (PVA) fiber, fiber content, particle size of rubber powder, and rubber powder content on the performance of CSM is analyzed, and the optimum mixing proportion is determined. Based on this, the modification mechanism of CSM by rubber powder and fiber is further studied from a micro perspective. The results show that the 7-day unconfined compressive strength of CSM gradually increases with the increase of fiber length. With the increase of fiber content, the compressive strength shows a trend of first increasing and then decreasing. The 7-day unconfined compressive strength of CSM gradually increases with the increase of rubber powder mesh size and linearly decreases with the increase of rubber powder content. The 28-day average dry-shrinkage coefficient of CSM shows a trend of first decreasing and then increasing with the increase of fiber length and fiber content, and gradually increasing with the increase of rubber powder mesh number and rubber powder content. Considering the strength and shrinkage characteristics, the optimum mixing parameters are 40 mesh rubber powder, 0.5 % rubber powder, 18-mm fiber length, and 1.2-kg/m3 fiber content. Scanning electron microscopy results show that there is a gap between the rubber powder and the cement matrix, and the interface between the two is discontinuous, with weak bonding, resulting in a decrease in the compressive strength of CSM. PVA fiber can improve the toughness of CSM. It has good adhesion with cement matrix. It forms a three-dimensional network support structure in the CSM mixture and can restrain water loss in the cement matrix, thus greatly improving the cracking resistance of CSM.

Synergetic Mechanism of Multiple Industrial Solid Waste-Based Geopolymer Binder for Soil Stabilization: Optimization Using D-Optimal Mixture Design

In order to improve the comprehensive utilization rate of industrial solid waste and the road quality, a novel low-carbon and environmental friendly soil stabilizer is proposed. In this study, steel slag (SS), carbide slag (CS), blast furnace slag (BFS), fly ash (FA), and desulfurized gypsum (DG) were used as raw materials to develop a multiple industrial solid waste-based soil stabilizer (MSWSS). The optimal mix ratio of the raw materials determined by D-optimal design was as follows: 5% SS, 50% CS, 15% BFS, 15% DG, and 15% FA. The 7-day unconfined compressive strength (UCS) of MSWSS-stabilized soil was 1.7 MPa, which was 36% higher than stabilization with ordinary portland cement (OPC) and met the construction requirements of highways. After 7 days of curing, the UCS of MSWSS-stabilized soil was significantly higher than that in the OPC group. X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) analysis indicated that the prominent hydration products were ettringite (AFt) and C-S-H gel. The results showed that an amount of AFt and C-S-H were formed in the initial stage of curing, resulting in a rapid improvement in early UCS. As the curing proceeded, the content of AFt and C-S-H increased constantly and grew intertwined with each other, which lead to the denser microstructure of stabilized soil and better mechanical strength.

Preparation and Mechanism Analysis of Stainless Steel AOD Slag Mixture Base Materials.

To promote resourceful utilization of argon oxygen decarburization (AOD) slag, this research developed a new three-ash stabilized recycled aggregate with AOD slag, cement, fly ash (FA), and recycled aggregate (RA) as raw materials. The AOD slag was adopted as an equal mass replacement for fly ash. The application of this aggregate in a road base layer was investigated in terms of its mechanical properties and mechanistic analysis. First, based on a cement: FA ratio of 1:4, 20 sets of mixed proportion schemes were designed for four kinds of cement dosage and AOD slag replacement rates (R/%). Through compaction tests and the 7-day unconfined compressive strength test, it was found that a 3% cement dosage met the engineering requirements. Then, the unconfined compressive strength test, indirect tensile strength test, compressive rebound modulus test, and expansion rate test were carried out at different age thresholds. The results showed that the mixture's strength, modulus, and expansion rate increased initially and then stabilized with age, while the strength and modulus initially increased and then decreased with increasing R. Secondly, based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) used to analyze the mechanism, it was found that the strength, modulus, and expansion rate of the new material can be promoted by blending AOD slag, due to its ability to fully stimulate the hydration reaction and pozzolanic reaction of the binder. Finally, based on the strength and modulus results, R = 3% was identified as the optimal ratio, which provides a reference point for the effective application of AOD slag and RA in road base materials.

Experiment investigation on mix proportion optimization design of anti-cracking stone filled with cement stabilized macadam

Semi-rigid base asphalt pavement is widely used in China for asphalt pavement construction. However, the presence of reflection cracks remains a significant issue associated with semi-rigid bases. Large Stone Filled with Cement Stabilized Macadam (LSFC) has been identified as an effective solution for inhibiting reflection cracks. However, the construction of LSFC using large particle size coarse aggregates can be challenging. Additionally, the existing mix design process lacks clarity and results in low strength. This paper aims to optimize the design method for anti-cracking Stone Filled with Cement Stabilized Macadam (SFC) by selecting appropriate materials and improving design process. Initially, a mix proportion for SFC is designed using coarse aggregates with common particle sizes employed in engineering applications. The filling proportion of the coarse aggregates, cement dosage, and mass proportion of the cement mortar are gradually determined through compaction and 7-day unconfined compressive strength tests, resulting in the complete mix proportion for SFC. Subsequently, the strength performance, fatigue performance, dry shrinkage performance, and temperature shrinkage performance of SFC are evaluated and compared with common Cement Stabilized Macadam (CSM). The results indicate that while the strength and fatigue properties of SFC are slightly inferior to those of common CSM, it exhibits superior dry shrinkage performance. Moreover, SFC demonstrates better overall crack resistance compared to common CSM, despite having slightly inferior temperature shrinkage performance.

Preparation of controlled low-strength materials from alkali-excited red mud-slag-iron tailings sand and a study of the reaction mechanism.

To address the low utilization of fines in iron tailings sand (IOTs), a controlled low-strength material (CLSM) was prepared from a combination of fine IOTs and red mud (RM) slag. The 7-day unconfined compressive strength (7-d UCS), slump and cost were used as evaluation indicators, and 16 sets of tests were designed with the Box-Behnken design (BBD) response surface method. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS) were used to study the microscopic morphology and reaction mechanism of the CLSM samples made with the optimal ratios. The results show that the best matching ratio for the alkali-activated RM-slag-IOTs CLSM was a sand ratio of 0.797, an NaOH dose of 3.667% and a mass concentration of 80.657%, and the 7d-UCS, slump and cost indicators verified the feasibility of applying the CLSM to the base course of pavement. Alkali activation of the CLSM also showed that the RM-slag cementation system produced new substances. Internal calcium-silicate-hydrogel (C-S-H) and calcium-aluminosilicate-hydrogel (C-A-S-H) agglomerates were the main sources of strength, and hydration products were interwoven to form a dense structure with crystals as the framework and gels as fillers.

Dewatering characteristics of waste slurry from pipe jacking based on improved vacuum filtration method

A large amount of waste slurry with high water content generated in the construction of slurry shield and pipe jacking needs to be reduced urgently. Due to high clay content of the waste slurry, existing treatment technologies such as plate and frame pressure filtration and vacuum filtration encounter problems such as low dewatering efficiency and low soil strength. Aiming at these problems, an improved vacuum filtration method was proposed and verified, which can transform waste pipe jacking slurry with high water content into soil material with certain strength while rapidly dewatering. The new method combines traditional vacuum filtration with curing technology. The experiment results show that after using the new method, the slurry with a water content of 400 % can rapidly drop to 62 % within 150 s, and 7-day unconfined compressive strength of the dewatered soil (q7day) can reach 117.33 kPa. The key mechanism of the improved vacuum filtration method was discussed. The pretreatment of solidification-flocculation increases the dewatering efficiency of vacuum filtration. The solidifying agent added in pretreatment still enhance strength of dewatered soil. Meanwhile, the strength formation mechanism of dewatered soil was proposed. The strength is related to water content of the dewatered soil (ωfinal) and the solidifying agent content (COPC).

Laboratory investigation of modified subgrade clay soil mix with steel slag and lime using static and dynamic test approach

ABSTRACT An experimental laboratory program was conducted to understand the feasibility of steel slag and lime in the subgradelayer. The test was conducted on natural clay soil, lime, lime + steel slag stabilizedcohesive subgrade soil. The lime portions were 2%, 4% and 6%, respectively.Similarly, steel slag was added to 20%, 25% and 30%, respectively, by the massof dry soil. The strength of lime soil and lime + steel slag + soil increaseswith increasing curing period. The 7-day unconfined compressive strength (UCS)2% lime soil and soil+20% steel slag + 2% lime is 3.20 MPa and 3.87 MPa,respectively. Eventually, this study supports the use of steel slag and lime inthe construction of subgrade stabilization. Therefore, it is found that a lightweightdeflectometer can be used as a quick strength evaluating tool on modifiedsubgrade soil in the laboratory.

Evaluation of strength development in cemented dredged sediment admixing recycled glass powder

Using glass powder (GP) as Portland cement (PC) helper in dredged sediment (DS) stabilization can achieve the double benefit of reducing PC dosage and recycling waste GP. This study evaluated the feasibility of using GP together with PC in improving the strength properties of DS. The effects of PC content, GP content, GP fineness and curing age on the strength development of PC-GP stabilized DS (CGDS) were investigated via a series of unconfined compressive strength (UCS) tests. Furthermore, scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests were conducted to analyze the strength evolution micro-mechanisms inside CGDS. The results showed that the UCS of CGDS increased monotonously with increasing PC content, and incorporating GP led to the strength gain of CGDS regardless of PC content. The optimum GP content tended to increase with increasing curing age and water content. The highest 28-day UCS of CGDS with water content of 50, 60 and 75% were respectively achieved at GP content of 15, 15 and 20%. Improving GP fineness can obviously improve the strength development of CGDS. The maximum strength growth rate (UCSgr) of CGDS with water content of 50, 60 and 75% were respectively achieved at PC content of 8, 8 and 10%, and increasing GP content and fineness resulted in UCSgr improvement. The 28-day UCS of CGDS can be predicted via the known 7-day UCS using proposed linear relation. The microstructural test results confirmed that incorporating suitable GP contributed to the formation of dense cemented soil matrix inside CGDS. The 10% PC admixing 15–20% GP with 2000-mesh number fineness is recommended to replace 15% PC for stabilizing DS containing 50–75% water content.

Experimental Study on Kaolinite Weathering Sand as Cement Mortar Accelerating Agent

In this study, the weathered sand from kaolinite mine in Yushan County, Jiangxi Province, China, was tested and analyzed in laboratory. XRD results show that montmorillonite is the main mineral composition of kaolinite weathered sand, and the content of montmorillonite is 35%. XRF test results show that the content of aluminum in weathered kaolinite sand is 9.8%. In order to explore the material properties of kaolinite weathered sand as cement mortar accelerating agent, the study compared the quick setting effect of kaolinite weathered sand with an accelerating agent and did the parallel test of 7-day strength of M10 grade mixed mortar. The results show that the 7-day unconfined compressive strength of kaolinite weathered sand fine sand mixed mortar test block is higher than that of accelerating mortar mixed mortar test block when the content of kaolinite weathered fine sand is equal to that of the accelerating agent. However, the 7-day unconfined compressive strength of mortar decreases when the content of fine-grained kaolinite weathered sand increases and the content of cement decreases, indicating that fine-grained kaolinite weathered sand cannot completely replace cement as cement mortar, and the proportion of fine-grained kaolinite weathered sand should be considered according to the strength grade of mixed mortar.

Optimal water-cement ratio of cement-stabilized soil

Since the water-cement ratio of cement-stabilized soil has a significant influence on strength and stiffness, this study aimed to investigate a new water-cement ratio selection method for deep soil mixing construction. An empirical model was established to estimate the optimal water-cement ratio of cement-stabilized soil with different cement contents based on the results of a series of liquid limit tests, bleeding limit tests, particle grading tests, unconfined compressive tests, and viscosity tests. The water-cement ratio calculated by this model can satisfy the fluidity of the cement-stabilized soil and prevent bleeding. The test results indicate that the optimal water-cement ratio changes with the cement content, and it can be accurately described by the proposed model. Besides, this model can also predict the 7-day unconfined compressive strength and stiffness of cement-stabilized soil with the optimal water-cement ratios. The cement-stabilized soil with the optimal water-cement ratio can guarantee the uniformity and strength. The proposed model shall be of practical value in dealing with the engineering problems on the selection of water-cement ratio in deep soil mixing construction.

An Experimental Study of the Road Performance of Cement Stabilized Coal Gangue

The research into the road performance of coal gangue is of great significance for the consumption of coal gangue and reducing pollution. In this paper, the coal gangues were prepared by separation and crushing processes, and their gradations were also optimized. Aiming to identify the possible problems of coal gangue as a pavement base, an unconfined compressive strength test, a splitting test, a freeze–thaw test, and a drying shrinkage test of cement stabilized gangue with varying cement amounts were carried out, and the test results were compared and analyzed. The test results showed that the maximum dry density and optimum moisture content (OMC) of the optimized cement stabilized gangue and cement stabilized macadam increased with cement content. The maximum dry density and OMC of cement stabilized macadam were larger than that of cement stabilized gangue with the same cement content. The optimized 7-day unconfined compressive strength of cement stabilized gangue can meet the requirements for a secondary and lower highway base and subbase. The OMC and cement content are the critical factors affecting the compressive strength loss rate of cement stabilized gangue after freeze–thaw cycles. The smaller the OMC of cement stabilized gangue and the larger the cement content, the lower the compressive strength loss rate. With an increase in cement content, the drying shrinkage strain of cement stabilized gangue increased. The results show that a cement content of 4% is optimal for the cement stabilized coal gangue, which can be used for the light traffic base and heavy traffic subbase of class II and below highways. It provides a basis, guide, and reference for the application of coal gangue materials in a high-grade highway base.

Experimental Study of the Mechanical and Microstructure Characteristics of Coal Gangue Road Stabilization Materials Based on Alkali Slag Cementation.

To accelerate the resource utilization of coal gangue and meet the strategic requirements of carbon neutralization, alkali-activated, slag-cemented coal gangue is applied in the preparation of solid waste-based road stabilization materials. Here, the cementation characteristics and microstructure characteristics of alkali-activated, slag-cemented coal gangue road stabilization materials are studied using the alkali equivalent and coal gangue aggregate ratio as experimental variables. The results show that with the increase in alkali equivalent from 1% to 7%, the unconfined compressive strength of the alkali-activated coal gangue road stabilization material initially increases and then decreases, with 3% being the optimal group in terms of stabilization, the aggregate ratio of coal gangue increases from 70% to 85%, and the 7-day unconfined compressive strength of the stabilized material decreases approximately linearly from 8.16 to 1.68 MPa. At the same time, the porosity gradually increases but still meets the requirements of the specification. With the increase in hydration time, a large number of hydration products are formed in the alkali slag cementation system, and they are closely attached to the surface of and interweave with the coal gangue to fill the pores, resulting in the alkali slag slurry and coal gangue being brought closer together.

Strength and Microstructure of Clay Geopolymer Non-Load-Bearing Masonry Units Using Fine-Clay Brick Waste and Palm Oil Fuel Ash

This research studies the applicability of alkali-activated cement with a mixture of fine-clay brick waste (FCBW) and palm oil fuel ash (POFA) to manufacture environmentally friendly masonry units. FCBW and POFA were used as a precursor, while a dredged soft clay (SC) was used as aggregate. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions were used as the liquid alkaline activator. Effects of NaOH concentration, initial SiO2/Al2O3 mole ratio, Na2SiO3/NaOH ratio, and curing conditions on the strength and microstructure of the FCBW-POFA-SC geopolymers were evaluated. The FCBW-POFA-SC geopolymers had a lower total unit weight than compacted SC because NaOH in the geopolymer binder caused a flocculated soil structure. It was found that Na2SiO3/NaOH=70/30, 10 M NaOH, and FCBW/POFA=70/30 were the best ingredients providing the rigid network of the geopolymer structures. The suitable heat duration of 48 h at 80°C accelerated the dissolution rate of the Si and Al and polycondensation in the geopolymer structure, resulting in denser geopolymer gels and early strength gain. With this optimum ingredient and suitable heat condition, 7-day unconfined compressive strength (UCS) of the FCBW-POFA-SC geopolymers achieved the requirement of the Thailand industrial standard for non-load-bearing masonry units (UCS>2.5 MPa). The geopolymer products were found to be sodium aluminum silicate hydrate (N─ A─ S─ H) and calcium aluminum silicate hydrate (C─ A─ S─ H). The research outcome will promote the usage of waste materials for manufacturing environmentally friendly infrastructure in Thailand and other countries.

Pavement Performance of Cement Stabilized Slag Base

In order to study the influence of power plant slag on the mechanical properties of cement stabilized macadam base, the cement stabilized macadam mixture was prepared by replacing natural stone with slag according to different proportion, and the compaction characteristics, unconfined compressive strength, splitting strength and compressive modulus of elasticity of the mixture were tested. The results show that the larger the amount of slag, the larger the optimal moisture content of the mixture and the smaller the maximum dry density; the 7-day unconfined compressive strength of the semi-rigid base layer increases first and then decreases with the amount of slag. Both the crack strength and frost resistance index decrease with the increase of slag content. The results prove that slag can be used as a substitute for aggregates in semi-rigid base course, which provides a test basis for the application of slag in road engineering.

Mechanical Characteristics of Stabilized Clay under the Influence of both Acidic and Alkalic Additives

To study the influence of the coexistence condition of acidic and alkalic additives on the mechanical performance of stabilized clay based on the processes for obtaining the basic physical parameters of soil and analyzing the stabilization mechanism of ionic and alkalic soil stabilizers, an experiment on the mechanical behavior characteristics of stabilized clay was performed using different types of ionic and alkalic stabilizers through a series of laboratory tests. The following results are obtained. (1) Typical soil is low liquid limit clay, and the ionic stabilizer with an optimal content of 0.014% mass ratio to dry soil exhibits strong acidity. (2) As a result of its unique molecular structure, the double electric-combined water film becomes thin rapidly during compaction molding, in which the compactness of clay particle structure increases. (3) The 7-day unconfined compressive strength can be improved with different contents of the ionic stabilizer. (4) Except for the high lime soil mixture, the compaction degree of soil exerts a pronounced effect on the stabilization performance of an ionic stabilizer and the least compaction degree should be over 96%. (5) The unconfined compressive strength, indirect tensile strength, and freeze-thaw performance of the acid-alkali-stabilized soil demonstrate a gradually increasing tendency with an increase in curing time, however, the evolution characteristic of strength exhibits an advantageous superposition threshold value when compared to the alkali-stabilized clay. The neutralization reaction and oil membrane of soil particles will inhibit the later reaction processes of carbonation, pozzolanic, and hydration of lime-|cement-stabilized soil.

Performances of Sandy Soil Stabilization with Fiber and Cement

To study the influence of polypropylene fiber on the strength of sandy soil stabilization with cement in flooded area of Yellow River, a series of experiments 7-day unconfined compressive strength have been done when samples reach 7-day standard curing. Based on the data, it is found that fiber content has an important influence than its length on unconfined compressive strength. As for failure modes, there are significant differences between the samples of adding fibers and those adding nothing. After adding 10 % cement, 1 fiber with 12 mm single length, the unconfined compressive strength of sandy soil stabilization with cement can be greatly improved with increase rate of 83%. It is concluded that the sandy soil can be successfully stabilized by the combined action of fibers and cement.

The Preliminary Study on Re-Utilization of Ferrous-Nickel Slag to Replace Conventional Construction Material for Road Construction (Sub-Grade Layer Improvement)

Ferrous-nickel slag is an industrial waste material which produced from smelting process of ferrous-nickel uses in manufacturing of stainless steel and ferrous alloy industry, in China Guangdong province itself, it was estimated around 6-7million of ferrous-nickel slag has been produces annually, the common method in order to reutilize ferrous-nickel slag material is by using on cement industry (replace cement material) and as land-filling material. One of the main objectives of this study is to investigate the feasibility of reutilization of ferrous-nickel slag combined with soil improvement method to portion replace conventional construction materials such as sand and granular material on sub-grade or sub-base layer of pavement construction. Strength and swelling properties of ferrous-nickel slag and soil (sand) mixture after treatment with soil improvement agent will be use as main consideration the performances of ferrous-slag nickel material on road construction, includes 4-days soaked California Bearing Ratio (CBR), 7-day Unconfined Compressive Strength (UCS) and also swelling behaviour of the mixture.

Performance and Utilization of Recycled Aggregates for Airport Cement Concrete Pavement

Cement concrete of airport pavement can be crushed into aggregates for recycle using, and the performance and utilizations of the recycled aggregates were discussed and researched herein. Sieve analysis indicated that the concrete should be crushed many times till the percentage of critical size (31.5mm) can satisfy the gradation requirements. Due to loss of crystal water, the density and water absorption of recycled aggregates were different from the natural ones, so that an empirical corretion equation was addressed subsequently. When the recycled aggregates used in the stablized base, theres no avilable method could yield the optimum water content, therefore a series of compaction and compression tests were employed to set up a modified design method. The results indicated the shrinkage property of recycled aggregates were susceptible to the moisture, either the skeleton-dense material structure and limiting the fine aggregates content were possible ways to eliminate the sensitivity. 7-day unconfined compressive strength results proved the recycled aggregates were suitble for the base course of heavy duty highways and airfield in grade E/F as well.

Factors Affecting Strength of Road Base Stabilized with Cement Slurry or Dry Cement in Conjunction with Full-Depth Reclamation

Full-depth reclamation (FDR) in conjunction with cement stabilization is an established practice for the rehabilitation of flexible pavements. Conventionally, the FDR process involves applying dry cement powder with a pneumatic spreader, but this process can create undesirable fugitive cement dust. To solve this problem, cement slurry has been proposed because it can allow cement stabilization to be used in urban areas. This research sought to (a) identify construction-related factors that influence the strength of road base treated with cement slurry in conjunction with FDR and quantify the effects of those factors and (b) compare the strength of road base treated with cement slurry with that of road base treated with dry cement. Full-factorial laboratory experimentation on a road base sampled from an FDR project was conducted. The 7-day unconfined compressive strength was measured as the dependent variable. The independent variables included cement content; slurry water batching temperature; presence of a set-retarding, water-reducing admixture; cement slurry aging temperature; cement slurry aging time; cement–aggregate mixing time; and form of cement. The results suggested that the slurry water batching temperature, the haul time, the environmental temperature, and the presence of a set-retarding, water-reducing admixture would not significantly affect the strength of a cement-treated base (CTB) within the ranges of the factors investigated in this research. However, cement content and cement–aggregate mixing time were found to be positively correlated with CTB strength, regardless of the cement form. Additionally, the use of cement slurry was found to result in slightly lower strength values than the use of dry cement.