Curing Period Research Articles

Hydration and Microwave Curing Temperature Interactions of Repair Mortars

Microwave curing of repair patches provides an energy efficient technique for rapid concrete repair. It has serious economic potential due to time and energy saving especially for repairs in cold weather which can cause work stoppages. However, the high temperatures resulting from the combination of microwave exposure and accelerated hydration of cementitious repair materials need to be investigated to prevent potential durability problems in concrete patch repairs. This paper investigates the time and magnitude of the peak hydration temperature during microwave curing (MC) of six cement based concrete repair materials and a CEM II mortar. Repair material specimens were microwave cured to a surface temperature of 40-45 °C while their internal and surface temperatures were monitored. Their internal temperature was further monitored up to 24 hours in order to determine the effect of microwave curing on the heat of hydration. The results show that a short period of early age microwave curing increases the hydration temperature and brings forward the peak heat of hydration time relative to the control specimens which are continuously exposed to ambient conditions (20 °C, 60% RH). The peak heat of hydration of normal density, rapid hardening Portland cement based repair materials with either pfa or polymer addition almost merges with the end of microwave curing period. Similarly, lightweight polymer modified repair materials also develop heat of hydration rapidly which almost merges with the end of microwave curing period. The peak heat of hydration of normal density ordinary Portland cement based repair materials, with and without polymer addition, occurs during the post microwave curing period. The sum of the microwave curing and heat of hydration temperatures can easily exceed the limit of about 70 °C in some materials at very early age, which can cause durability problems.

Experimental Investigation of a Novel Formulation of a Cyanoacrylate-Based Adhesive for Self-Healing Concrete Technologies

The selection of an appropriate healing agent is critical to the success of vascular and mini-vascular networks. In self-healing concrete technology, commercially available cyanoacrylate (CA) adhesives have been shown to produce good strength recoveries; however, their rapid curing rate and short shelf-life make them unsuitable for site application. The aim of this study was to develop a modified cyanoacrylate (n-CA) with an extended shelf-life suitable for incorporation in a self-healing system. A series of n-CAs were formed from a commercial Ethyl Cyanoacrylate adhesive mixed with acrylic acid (AA) and nitro-anthraquinone (nAq) in varying ratios. When encapsulated within 3D printed mini-vascular networks (MVNs), the n-CAs remained dormant in liquid form for up to 5 days. The contact angle between the n-CAs and the cement mortar substrate, as measured via the sessile drop technique, decreased significantly with increasing AA content. The mechanical properties (bond strength) and the polymerization hardening of the n-CAs were evaluated over a curing period of 7–21 days, via a series of pull-off tests using cement mortar cubes. The 4:1:02 (CA:AA:nAq) n-CA formulation showed a significant increase in bond strength from 14 to 21 days, with a ceiling value of 2.6 MPa, while the 2:1 (CA:AA) n-CA formulation exhibited a good bond strength after 21 days (1 MPa). Nuclear Magnetic Resonance (NMR) conducted on the n-CAs suggested the formation of several new polymeric species, whilst differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) on the pre- and post-printed MVN material confirmed no significant changes in chemistry with no evidence of polymer degradation. Considered together, the experimental results show the potential for different n-CA formulations to act efficiently as a healing agent.

Performance-Based Approach for Deciding the Age of New Concrete for Thin Epoxy Overlay Application

A thin epoxy overlay application is a capital preventive maintenance activity. Epoxy overlays reduce the rate of chloride ion ingress and extend bridge deck service life. Highway agency policies and manufacturer specifications require maintaining a 28-day curing period (7-day wet and 21-day dry curing) before the application of an epoxy overlay on bridge decks requiring new concrete for patches and repairs. Consequently, the contractors wait for 28 days to apply an epoxy overlay. Delaying application time increases project completion time and the cost of construction and mobility. The suitability of new concrete to receive epoxy overlays and the performance of overlays depend on several parameters including concrete strength, moisture, and tendency to crack. Such parameters depend on concrete mixture ingredients and wet and dry curing periods. This paper presents a performance-based procedure for evaluating the possibility of reducing the 28-day waiting period for a thin epoxy overlay application on new concrete. An experimental program was developed and executed to evaluate the impact of epoxy overlay application parameters and overlay performance using a tensile bond pull-off strength test. The results support developing a performance-based procedure for deciding on the suitable age of new concrete to receive a thin epoxy overlay. The pull-off bond strength of epoxy overlays applied at 7, 14, and 21 days, following a 7-day moist curing, shows the possibility of applying an epoxy overlay before the end of the 28-day curing period stipulated in the current specifications.

Dilution of Biogas Bioactivator to enhance microbial growth

The addition of bioactivator to biogas unit is a breakthrough to accelerate and increase the formation of gas. Bioactivator are made from fruit waste that is commonly found in local markets, including bananas, papaya and pineapples. This study aims to find the level of fruit waste dilution to obtain consistency that supports an ideal environment for microbial growth in biogas unit. Fifteen treatments on 15 plastic containers contain fruit waste with a dilution rate of 1, 2 and 3 times with a curing period of 25 days. The parameters were bioactivators colour and smell, pH, and microbial population of bacteria and fungi. The study result was that treatment with dilution rate of 3 times gave better result than other treatments. Bioactivator colour was yellow to orange with tapai/alcohol odour. The pH varies from 3.1 to 4.2. The largest microbial population were as follows bacteria 9.45x107 cfu/ml and fungi 12.32x105 cfu/ml.

The electro-mechanical tensile properties of an engineered cementitious composite

The influence of ongoing cement hydration and multiple microcrack formation on the electrical impedance of an engineered cementitious composite (ECC) is presented. Impedance measurements were obtained over the frequency range 20 Hz–1 MHz and displayed in the Nyquist format. In addition, the permittivity and conductivity were de-embedded from the measured impedance and presented in both time and frequency domains to elucidate the nature of conduction and polarisation processes. It was found that, over a curing period of 90 days, the ECC displayed a classic impedance response. Both conductivity and relative permittivity were found to be frequency dependent due to bulk relaxation processes operating within the composite. Tensile straining was shown to result in a detectable change in the impedance response, but retained a similar overall profile. When presented in the frequency domain, a downward displacement in both conductivity and relative permittivity profiles was evident with increasing tensile strain. It is shown that the relative permittivity at the high-frequency end could be exploited as a potentially useful indicator for strain/damage detection. The influence of microcracking on the piezo-resistive response of the composite is discussed based on crack patterns obtained from both visual observations and digital image correlation.

Using of recycled clay brick/fine soil to produce sodium hydroxide alkali activated mortars

In the study, the recycled clay brick powder/fine soil powder-based sodium hydroxide alkali-activated mortar (AAM) specimens were prepared by mixing different percentages (100/0, 80/20, 60/40, 40/60, 20/80, and 100/0, respectively) to investigate the mechanical and durability performance of sustainable AAM specimens for the possible utilization instead of OPC. The constant ratio of glass powder was used in the production of AAM to increase the alkalinity and improve the mechanical properties of alkali-activated mortar. Also, the influences of sodium hydroxide molarity concentrations (8, 10, 12, 14, and 16 M) on the performance of AAM specimens were studied. The compressive strength, water absorption, and water sorptivity tests were conducted on the AAM specimens and the relationships between the investigated parameters were analyzed. The obtained results revealed that the fine soil powder replacement with clay brick powder improved the compressive strength, and reduced water absorption and water sorptivity up to 80% replacement ratios, and the superior mechanical and durability performance was obtained in the 80% fine soil powder-based AAM specimens. For the higher fine soil powder replacement ratio (100%), the performances of the AAM specimens were found to be adversely affected. Besides, the concentration of NaOH solution significantly influenced the material performances of the fine soil powder-based AAMs and 12 M NaOH concentration performed superior mechanical and durability performance. The strength enhancement of the AAMs was found to be significant after 90 days of ambient curing period.

Study on the Mechanism of Stabilizing Loess with Lime: Analysis of Mineral and Microstructure Evolution

X-ray diffraction (XRD) technique was adopted to test the mineral composition of quicklime-solidified loess with different lime-adding rates at different curing periods. Scanning electron microscopy (SEM) and nitrogen adsorption were used to analyze the microporous structure of the solidified loess. The unconfined compressive strength and limit moisture content of solidified loess were combined to analyze the evolution mechanism of mineral composition and microstructure of solidified loess with the change of curing period and clarify the mechanism of quicklime-solidified loess. The results showed reduced content of clay minerals and decrease in the number of large pores due to increase of hydrates and pozzolanic products during extended curing period. The solidified soil fabric transformed from a compact structure into a mesh structure composing of acicular crystal and cementation. The main reasons for strength increase and change of liquid and plastic limits with the lime-solidified loess after extended curing are the change of the substance and the microstructure.

Development of eco-efficient lightweight self-compacting concrete with high volume of recycled EPS waste materials.

Reusing the industrial waste materials is one of the main aims of sustainability and achieve the environmental protection. However, concrete is the main production for recycling waste materials and cleaning the climate. The utilization of self-consolidating lightweight concrete (SCLC) can achieve two important advantages of the structure self-weight reduction and improving workability. This paper examined the effect of waste expanded polystyrene (EPS) beads on the workability and hardened characteristics of sustainable SCLCs. Six different EPS volume fractions up to 80% replaced with normal coarse aggregate to produce SCLC mixtures with water to binder (w/b) ratio of 0.35. A total binder content of 500 kg/m3 by including 20% waste ceramic powder with 80% Portland cement and fine aggregate consist of river sand and fine ceramic with 1:1 ratio in all SCLC mixes. The workability of SCLCs was examined by slump flow time and diameter, L-box height ratio, V-funnel flow time, and segregation resistance. Moreover, the hardened properties tested at different curing periods such as compressive strength at 7, 28, and 90 days; flexural strength at 28 and 90 days; and splitting tensile strength, dry density, voids percent, water absorption, ultrasonic pulse velocity (UPV); and scanning electron microscope (SEM) at 28 days. The results verified that workability of SCLCs enhanced as EPS incorporation increased and achieved the limitations required for self-compacting concrete (SCC) while the strengths value curtailed but the compressive strength satisfied the lower value indicated by ACI for structural purposes. Depending on the water absorption and UPV, results illustrated that all produced sustainable SCLC mixtures had a good durability. Furthermore, a high linear correlation was noticed between the results.

Recycled Glass Cullet as Fine Aggregate and Partial Cement Replacement in Concrete

Utilisation of recycled glass cullet in concrete has obvious benefits with respect to environmental conservation and sustainable development. The problems of rising landfills can be reduced. Reduction of primary aggregates for concrete where alternative materials would suffice can also be fulfilled. Glass also contains large amounts of silicon and calcium which means that in theory, is pozzolanic. However, the possibility of alkali-silica reaction (ASR) due to the presence of silica must also be addressed. Tests were performed to investigate the suitability of using cullet in concrete. A sieve analysis was performed to determine the size distribution of the cullet and provided basis to the range of samples that could be cast. Using cullet as partial replacement aggregate in concrete has resulted in minor increases in concrete consistence (workability) and minor reductions in compressive strength. When ground glass cullet (GGC) was used as 30% partial cement replacement, the consistence increased considerably, whilst the later age compressive strength was close or higher (depending on the mix proportions used) compared to the corresponding control mixes, which did not have GGC incorporation. The early age strength was lower and strength development was slower at early ages further suggesting likelihood of pozzolanic activity. Accelerated ASR tests have shown the occurrence of ASR in concrete mixes using cullet as replacement aggregate to be more than control mixes which used conventional aggregate. The magnitude of ASR was also found to be colour dependant-green coloured cullet resulted in less expansion than when using amber cullet. Qualitative microstructural analysis of specimen micrographs recorded in Secondary Electron Imaging (SEI) mode using a Scanning Electron Microscope (SEM) have shown that mortar specimens using cullet displayed more cracking at longer curing periods. Cracks propagated from, and surrounded the glass particles, further suggesting the occurrence of ASR activity. Depending on size classification used, glass cullet can therefore be recommended to be used as partial aggregate replacement and partial cement replacement in concrete. The possibility of durability attack due to ASR reaction must however be taken into consideration.

The Strength Behaviour of Eggshell Powder Substitution on Soil-lime Stabilization

This study explored the investigation into enhancing soil strength characteristics using eggshell powder (ESP) as a lime substitution on soil-lime stabilization. The ESP was naturally available while using this material, which could reduce cost and other environmental effects. The influence of varying percentages of eggshell powder as a lime substitution in changes of the strength and durability is observed based on the unconfined compression test conducted on two soil and two lime types (hydrated lime and quicklime). Influence factors were studied, including soil and lime types, ESP content, curing time, and durability against wetting-drying (w-d) cycles. The unconfined compressive strength (UCS) and the durability values of ESP-stabilized soils decreased, while ESP content increased. However, this value was higher than the unstabilized ones. The ESP substitution on soil-lime stabilization marginally affected the strength and durability of soil-lime stabilization. The UCS increased with the increasing curing period for all specimens. Soils with more clay particles reacted better to both hydrated lime and quicklime. Additionally, strength development occurred in soil-quicklime mixtures more than in soil-hydrated limes. Based on a durability test, it was known that the maximum ESP substitution was 50% from the Optimum Lime Content (OLC); beyond that content, the strength of soil might dramatically be degraded.

Evaluating the Durability of Lime-Stabilized Soil Mixtures using Soil Mineralogy and Computational Geochemistry

Lime stabilization is a common technique used to improve the engineering properties of clayey soils. The process of lime stabilization can be split into two parts. First, the mobilization and crowding of [Formula: see text] ions or [Formula: see text]molecules from hydrated lime at net negative surface charge sites on expansive clay colloids. Second, the formation of pozzolanic products including calcium-silicate-hydrate (C-S-H) because of reactions within lime-soil mixtures. The pozzolanic reaction is generally considered to be more durable, while the [Formula: see text] adsorption has been associated with more easily reversible consistency changes. This study offers a protocol to assess whether the stabilization process is dominated by durable C-S-H (pozzolanic) reactions or a combination of cation exchange and pozzolanic reactions. Expansive clays with plasticity indices >45% from a major highway project in Texas are the focus of lime treatment in this study. The protocol consists of subjecting lime-soil mixtures to a reasonable curing period followed by a rigorous but realistic durability test and investigating the quality and quantity of the pozzolanic reaction product. Mineralogical analyses using quantitative X-ray diffraction (XRD) and thermogravimetric analysis (TGA) indicates the formation of different forms of C-S-H. In addition, geochemical modeling is used to simulate the lime-soil reactions and evaluate the effect of pH on the stability of C-S-H. The results indicate C-S-H with Ca/Si ratio of 0.66 as most the stable form of C-S-H among other forms with Ca/Si ratio ranging from 0.66 to 2.25. The effect of reducing equilibrium pH on C-S-H is also evaluated. A reduction in pH favored dissolution of all forms of C-S-H indicating the need to maintain a pH ≥ 10.

Pengaruh Penambahan Fly Ash Terhadap Perilaku Teknis Tanah Ekspansif di Daerah Selimau Kabupaten Bulungan

Expansive soil is one of the problematic soils for civil engineering construction. The high swelling-shrinkage nature results in deformations that can damage the construction on it, therefore it is necessary to make improvements in expansive soil. One of the most widely used methods of improving expansive soil is stabilization using chemical additives. In this research using coal waste material (fly ash) as stabilizer from PLTU Sekayan in Kaltara Province, so it can be said as environmentally friendly stabilization. The research objective was to determine changes in engineering behavior of expansive soil through compaction tests and CBR. The test results will be displayed in graphical form, namely by comparing the expansive soil that has not been stabilized (initial conditions) and the expansive soil that has been stabilized with fly ash at mixed variations of 20%, 30% and 40%, and has passed the curing period for 5, 15, and 30 days. From this research, it was found that the addition of a stabilizer (fly ash) could improve its engineering properties, and the optimum results were obtained at the addition of 40% fly ash and after 30 days of curing time. From the compaction test, it was found that the volume weight of dry soil (γdry) increased by 14.05% from 1.21 gr/cm3 to 1.38 gr/cm3 and the optimum water content (wopt) decreased by 38.12% from 31.19% to 19,3%. From CBR testing in the laboratory, there was a very large increase in the value of CBRDesign, namely 2192% from 0.72% to 16.5%

Improvement of shear strength and compressibility of soft clay stabilized with lime columns

Soft clay improvement using lime columns is an effective and economic method; which used mainly for enhancing the engineering properties of soft soil, reducing settlement and increasing shear strength. Improvements in engineering properties of soft clay can be achieved instantaneously with small additions of lime to soft soils. However, the effectiveness of this improvement depends on the quantity and type of lime as well as the mineralogical composition of soil. In this paper, the behavior of soft clay improved with lime columns has been studied. A series of large scale direct shear box tests were carried out with different number of lime columns, diameter, and different curing periods. Experimental study was carried out on both single and a group of lime columns. The results showed that the group of columns increased the shear resistance of soft clay soil with lesser horizontal deformation. Shear strain decreased by 28% and 47% in case of using 1 and 4 lime columns respectively after 7 days curing. Meanwhile, increasing the lime column diameter was found to increase the shear strength of soft clay and improve its compressibility. Finally, the shear strength was found to be increased by 53% when using a single lime column, while when using a group of 4 lime columns with diameter/length (D/L) ratio equals 0.28, the shear resistance is duplicated compared to the case of soft clay without lime columns.

Experimental study on addition of Steel Fibres in Conventional Concrete

Fibre Reinforced Concrete (FRC) is a composite material which consists of constituents of conventional concrete along with the addition of fibres. The two major classifications of fibres are natural and artificial fibres. The main purpose of use of fibres in concrete is to arrest the formation and propagation of cracks in concrete. The purpose of this study is to compare the mechanical properties of Steel Fibre Reinforced Concrete with the Conventional Concrete. Steel fibres with four different percentages such as 0.5%, 1.0%, 1.5% and 2.0% were added to the concrete. Three different grades of concrete such as M40, M50, M60 were experimented in this study. Compressive strengths of cube specimens were calculated for these dosages with a curing period of 14 and 28 days. Optimization of the SFRC was done through the Compressive strength test results. It was observed that fibre dosage of 1.5% showed maximum values when compared with other percentages. With the optimized percentage of Steel Fibre, split tensile strength test was carried out. It was observed that the addition of steel fibres in concrete improved the compressive strength and split tensile strength of steel fibre reinforced concrete. At 28 days of curing with the addition of 1.5% of fibres, the compressive strengths of M40, M50 and M60 grades of concrete increased by 14.6%, 13.7% and 11.8% respectively compared with conventional concrete. Similarly, at 28 days of curing with the addition of 1.5% of fibres, the split tensile strengths of M40, M50 and M60 grades of concrete increased by 7.66%, 8.59% and 9.23% respectively compared with conventional concrete. In addition, a microstructural analysis was done to determine the material characterisation through Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD).

Experimental Investigations on the Mechanical Properties of Sand Stabilized With Colloidal Silica

Colloidal silica is an innovative stabilizer that is being explored in ground engineering fields. Several experimental investigations were performed to study the effects of colloidal silica stabilization on shear strength as well as hydraulic conductivity of sand. The main aim of the present work is to observe the enhancement in the mechanical properties of colloidal silica-stabilized sand. The paper also aims to explore the optimum pH and corresponding salt content, which provides workable gel time in the field. The primary objective of the present work is to determine the gel time of the colloidal silica solution by adding salt and varying pHs. It was observed that the gel time decreases rapidly as the ionic strength of the colloidal silica solution increases. Sand having relative densities (RD) of 30, 40, and 60% stabilized with four different colloidal silica percentages under a curing period of 3, 7, and 28 days were tested. All test specimens were tested as per standard codal procedures to determine the optimum content of colloidal silica for the enhancement of the mechanical properties of sand. Based on test results, the optimum percentage of colloidal silica at 30% RD, 40% RD, and 60% RD was found to be 12.5%, 11%, and 10%, respectively. Moreover, significant enhancement was observed in the shear strength as well as hydraulic conductivity with the addition of colloidal silica in the sand.

Effectiveness of fresh cement kiln dust as a soil stabilizer and stabilization mechanism of high swelling clays

The expansive clay soils, which cover most of the new urbanized areas in Egypt, create major damages in most of the engineering structures and infrastructures such as buildings, roads, bridges, pipelines and others due to bad human activities, e.g. lack of maintenance for sewage and drinking lines, and flood irrigation of golf areas which causes fluctuation of water content through the foundation clay layers associated with shrink-swell behavior. These geotechnical challenges and their treatment solutions consume most of the urbanized project budget and delay the development plan. Therefore, in this study the high plasticity and soft to firm clay soils were stabilized using various dosages of fresh cement kiln dust (CKD) as an economical alternative to the other expensive stabilizing agents (stabilizers or binders) such as lime, cement and other chemical stabilizers. The effectiveness of this type of CKD as a stabilizing agent, soil stabilization mechanism, and changes in mineralogical and microstructural characteristics of stabilized soils due to this stabilization process were evaluated through Atterberg limits, unconfined compressive strength (UCS), stiffness (stress–strain behavior, Es), pH, electrical conductivity (EC), total dissolved solids (TDS), X-Ray diffraction (XRD) and scanning electron microscope (SEM) investigations. The present study revealed that by adding CKD, the workability of the treated clays was increased by decreasing the liquid limit and plasticity index as well as increasing the bearing capacity and decreasing the settlement by increasing UCS and Es. This study also showed that by adding CKD, the initial pH, EC, and TDS of CKD-clay system increased, creating favorable conditions for dissolution of edges and surfaces of clay flakes. The active montmorillonite clay flakes adsorbed the soluble calcium cation and sulfate anion on their surfaces that are rich in soluble silica and alumina and then the cation exchange and flocculation–agglomeration processes began. With curing, the pozzolanic products grew on the surfaces and edges of clay flakes and extended into the voids of the agglomerated inter-clay particles resulting in the filling of these micro-voids. The present investigation also found that, the progressive decreasing in pH, EC, and TDS values of CKD-clay systems through different curing periods is a good indicator for pozzolanic activity.

Improvement of Strength and Volume-Change Properties of Expansive Clays with Geopolymer Treatment

Expansive soils are conventionally treated with chemical stabilizers manufactured by energy-intensive processes that significantly contribute to carbon dioxide emissions globally. Geopolymers, which are synthesized from industrial byproducts rich in aluminosilicates, are a viable alternative to conventional treatments, as they are eco-friendly and sustainable. In this study, a metakaolin-based geopolymer was synthesized, and its effects on the strength and volume-change behavior of two native expansive soils from Texas, with a plasticity index over 20 were investigated. This paper elaborates on the geopolymerization process, synthesis of the metakaolin-based geopolymer, specimen preparation, and geopolymer treatment of soils. Comprehensive material testing revealed two clays with a plasticity index over 20. They were each treated with three dosages of the metakaolin-based geopolymer and cured in 100% relative humidity for three different curing periods. The efficiency of geopolymer treatment was determined by testing the control and geopolymer-treated soils for unconfined compressive strength (UCS), one-dimensional swell, and linear shrinkage. Field emission scanning electron microscope (FESEM) imaging was performed on the synthesized geopolymer, as well as on the control and geopolymer-treated soils, to detect microstructural changes caused by geopolymerization. A significant increase in UCS and reduction in swelling and shrinkage were observed for both geopolymer-treated soils, within a curing period of only 7 days. The FESEM imaging provided new insights on the structure of geopolymers and evidence of geopolymer formation in treated soils. In conclusion, the metakaolin-based geopolymer has strong potential as a lower-carbon-footprint alternative to conventional stabilizers for expansive soils.

Assessing the effect of moulding water content on the behaviour of lime-stabilised an expansive soil

ABSTRACT There are several factors that affect the efficiency of soil stabilisation and their strength gain. In fact, the proportion of mixing is one of these factors which include mixing conditions, degree and timing of mixing, the quantity of hardening agent and moulding water content. An experimental study was undertaken in order to assess the effect of moulding water content (MWC) on some geotechnical properties of lime-stabilised an expansive soil. Lime was mixed with the studied soil within the range of 0% to 8%. All samples were performed according to three different conditions at different curing periods. The obtained results showed that the increase in lime content reduces the maximum dry density (MDD) and increases the optimum moisture content (OMC) where the increase in lime content causes a decrease in the specific gravity (Gs) with an increase in the void ratio. The unconfined compressive strength (UCS) of lime-treated high plastic clay increases with increasing lime content for the different conditions. Also, samples prepared at OMC and MDD develop very high UCS values compared to those prepared with a dry and wet side of optimum.

Experimental study on unconfined compressive and cyclic triaxial test behavior of agar biopolymer–treated silty sand

The need for space for infrastructure development has plummeted studies in ground improvement to an eminent research topic. But in the present day where the need for sustainability is of utmost importance, efficient and environment-friendly improvement methods have been coming up among which the use of biopolymers as a soil additive have gained popularity. In the current research, various strength aspects of agar biopolymer–treated silty sand soil have been explored. The unconfined compressive strength property of treated silty sand at varying agar dosages (0.5%, 1%, and 2%) at different curing periods (3 days, 7 days, and 28 days) was analyzed using laboratory investigations. Furthermore, the effect of frequency of loading on dynamic properties and pore pressure response of the agar-treated silty sand was also investigated by performing a set of strain-controlled cyclic triaxial test at different frequencies (0.2 Hz, 1 Hz, 1.5 Hz, and 2 Hz). The tests were performed at constant axial strain amplitude of 1% and at confining pressure of 100 kPa. The results demonstrated that with the increase in agar content and curing time, the unconfined compressive strength of soil also increased. Besides, a decrease in pore pressure build-up, decrease in secant shear modulus, and an increase in damping was observed on increasing the frequency of cyclic loading.

Discrete fiber reinforcement efficiency in the mechanical properties and wet-dry performance of fat clay treated with industrial sewage sludge ash

This paper presents a laboratory evaluation of the strength and durability behavior of treated clay with industrial sewage sludge ash (ISSA) and Polyvinyl alcohol (PVA) fiber. Unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) tests were conducted on treated clay with different percentages of ISSA and short PVA fiber content after different curing period to evaluate strength properties. In this study, UPV tests were used as a non-destructive method to determine the optimum curing period. The UCS test results indicated that the ISSA inclusion caused an increase in UCS values and a decrease in the axial strain at failure, while fiber inclusion within the ISSA treated soil increases UCS and failure strain, hence decreases brittle index. A good correlation of UPV values (P-wave velocity or VP) and UCS test results is seen by an exponential function. The microstructure of untreated and ISSA treated soil as well as the interaction between PVA fiber surface and ISSA treated soil matrix were investigated by scanning electron microscopy (SEM) tests and image processing analysis. SEM images show that soil porosity increases with the addition of ISSA and, the created scratches and formation of cement bonding on fiber surface increase the interlocking force. This study also assessed the durability of ISSA treated and fiber-reinforced soil against wetting–drying (W–D) cycles. UCS and UPV tests were performed after wetting–drying cycles for this study. Results showed that in ISSA treated soil with fiber inclusion, strength increased with an increase in W-D cycles from zero to three cycles and decreased afterward.