Curing Time Periods Research Articles

Effect of Curing Temperature under Deep Mining Conditions on the Mechanical Properties of Cemented Paste Backfill

Nowadays, the cemented paste backfill mining method is widely used in mines. Since the temperature of the mine increases with increasing mining depth, the influence of temperature on the mechanical properties of cemented paste backfill (CPB) require attention. To address the problem of less research on paste performance in high temperature environments, uniaxial compressive strength tests of CPB at different temperatures were performed, and it was observed that temperature had a significant effect on the CPB strength. The CPB strength at a curing temperature above 40 °C deteriorated in the later curing time period, CPB at 65 °C was “crisp”, and the strength was lower than 40 °C in 3~28 days. Microscopic tests, such as thermogravimetric analysis (TGA/DTG), X-ray diffraction (XRD) and scanning electronic microscopy (SEM) analysis, of the samples found that the coarsening of the pore structure of CPB was the main reason for the decrease in the strength caused by the increase in temperature. The effect of curing temperature on the deformation characteristics of CPB was studied. Different curing temperatures had a greater impact on the stress-strain curve and elastic modulus, and there was a linear relationship between the elastic modulus and strength. Finally, based on MATLAB, a back propagation (BP) neural network model of strength under different curing temperature conditions was established. Compared with the actual value and the predicted value, the average absolute error was less than 0.2 MPa, and the average relative error was less than 6%. This prediction model had a high accuracy. The research results provide a good reference significance for the strength design of CPB.

Evaluation of Strength Properties of the Concrete Prepared from Class F Fly Ash

Cement is a hazardous and expensive material that is used in the production of concrete, where the cost of the concrete is minimized by replacing the cement with similar cementitious materials. According to the report of the national thermal power corporation, the production of fly ash is rising each year as a result of increasing demand for electricity. In this research paper, an attempt has been done by replacing cement with fly ash as an alternative material. The concrete samples are prepared with different compositions by using different percentages (0%, 10%, 20%, 30%, 40%, 50%, and 60%) of fly ash. In this research, the behaviour of the fly ash concrete is investigated by different strength-related properties; compressive strength, splitting tensile strength, and flexural strength at various curing time periods of 7, 28, 56, 90, and 180 days. In the experimental section, the developed fly ash concrete obtained maximum compressive strength of 83.50N / mm 2, a flexural strength of 6.60N / mm 2 and a splitting tensile strength of 4.90N / mm 2 on the 180th day in the composition of 450kg/m 3 and 0.4W/B ratio. Percentage gain of compressive, split tensile and flexural tests for 450 kg/m3 at 0.4 W/B ratio at 180 days curing is 13%, 9% and 13% with 30% fly ash replacement when compared to 350 kg/m3 binder content. Proportional increase of cement content also leads to increase fly ash content in concrete. Fly ash has potential of filling pores because of having finer particles and performs pozzolanic action which resulted in attaining high strength even after optimum replacement when compared to conventional concrete.

Permeability of Expansive Soils Modified/Stabilized with lime (Review Paper)

The aim of this paper was to review the mechanism of the expansive soil-lime reactions: short term and long-term reactions in both lime modification and lime stabilization. The focus of the study was the effect of curing time for a certain centigrade 25C curing temperature in both lime modification / stabilization-expansive soils on the coefficient of permeability. Peer reviewed articles published between 2000- and 2019 were collected and relevant data were extracted. Results of this review study showed that the coefficient of permeability of expansive soils modified with lime increased during the first 7 days of curing time at curing temperature 25C and it remains constant or slightly decreased for longer curing time periods. However, for expansive soils stabilized with lime, it was found that the coefficient of permeability increased during the first 7-day curing time at curing temperature 25C, then decreased during the longer curing time periods (pozzolanic reaction). It is also noted that even though the coefficient of permeability decreased during pozzolanic reaction, it remains higher than that of the untreated soils

Ageing effect on compressibility, permeability and shear strength of clayey soils exposed to salt solutions

The present study investigated the ageing effect on compressibility, permeability and shear strength behavior of kaolin and bentonite samples in the presence of NaCl and CaCl2 solutions. The compressibility, permeability and shear strength parameters were determined on the 60, 190, and 250 days cured samples. The results have shown that, the kaolin sample becomes more compressible in the presence Ca2+ ions with ageing. Generally, the normalized compression index values of bentonite samples increased at the end of 60 days and 250 days curing time periods. The normalized permeability value of kaolin decreased by ageing in the presence of Na+ ions almost twofold. The permeability values of bentonite increased both in NaCl and CaCl2 solutions during ageing. In the presence of Na+ ions kaolin had higher max. shear stress value than Ca2+ ions. When the max. shear stress values of 0, 60 and 190 days samples were compared, it was seen that NaCl solution had no significant effect on the shear strength of kaolin sample. However, the shear strength of kaolin increased in the CaCl2 solution during ageing. In the presence of Ca2+ ions the max. shear stress value of bentonite was higher. The results of this study have shown that ageing has significant effects on the compressibility, permeability and shear strength of kaolinitic and bentonitic clayey soils.

Triaxial test behaviour of silty sands treated with agar biopolymer

ABSTRACT In the current research, the study of undrained behaviour of agar biopolymer treated natural silty sand obtained from Kalpetta, Kerala was done. An experimental investigation was carried out to study the undrained behaviour of silty sand and biopolymer treated silty sand for examining the efficiency of agar biopolymer additive on undrained shear strength improvement. The practical implications of biopolymer treatment have also been evaluated. A series of consolidated undrained monotonic triaxial tests were performed at varying confining pressure (50 kPa, 100 kPa and 150 kPa), agar dosages (0.5%, 1% and 2%) and curing time periods (5 hours, 1 day, 3 days, 7 days and 28 days) to evaluate the efficiency of treatment. The treatment method displayed a considerable enhancement in shear strength behaviour (about 106% increase) mainly due to the significant amount of cohesion developed in the cohesionless soil under study.

Control the crosslinking of epoxy-asphalt via induction heating

ABSTRACT Induction heating driven polymerisation is an in-situ curing technique for epoxy-asphalt systems that maintains most of the advantages of temperature-driven polymerisation and it solves the need for longer curing time periods at lower temperatures before traffic can be allowed. In particular, induction heating can be utilised to accelerate the polymerisation of paving mixes with a thermo-hardening nature. In this study, steel fibres are dispersed in a mix and during exposure to an alternating electro-magnetic field generated by induction coils, they are heated leading to the rapid initiation of epoxy-asphalt polymerisation. This research presents the implementation of a finite element model analysis for assessing the potential of utilising steel fibres for the development of inductive mixes with sufficient induction heating efficiency. A produced and compacted mix with steel fibres was reconstructed by means of CT scans on samples from the mix and its effective electrical conductivity was calculated. Also, the electro-magnetic induction-driven polymerisation of epoxy-asphalt is simulated by extending a model developed elsewhere. The extended method can be used to predict the evolution of the curing process, and further of mechanical properties thereby indicating that electro-magnetic induction represents a reliable polymerisation method to cure epoxy-asphalt systems.

Modeling of compressive strength of cemented sandy soil

This paper attempted to show the application of particle swarm optimization in the prediction of the compressive strength of cement sandy soil from the curing period, porosity of sample and percentage of cement. The results of the study show that the unconfined compressive strength of the cement stabilized sandy soil increases with an increasing cement content curing time period. Moreover the compressive strength decreases with an increasing porosity. The compressive strength improvement due to cement treatment has a larger increase in samples with less porosity. In addition, particle swarm optimization algorithm is and accurate technique in estimation of compressive strength of cement stabilized sandy soil. In order to compare of existing correlations, a total number of 100 unconfined compressive tests and 15 scanning electron microscope tests have been conducted on cemented Babolsar sand. It can be concluded that compared to existing correlations models, particle swarm optimization algorithm models give more reliable prediction about compressive strength of cement satblized sandy soil. Moreover, the sensitivity analysis of the polynomial model shows that cement content and porosity have significant impact on predicting unconfined compressive strength.

Definition of optimal parameters for supercritical carbonation treatment of vegetable fiber-cement composites at a very early age

This paper presents a study of cellulose pulp fiber-cement composites subjected to supercritical carbonation at a very early age. The raw materials used for the creation of cementitious composite mixes include: Portland cement, limestone filler, and cellulose pulp. Composites were produced by a slurry vacuum dewatering process and subjected to curing conditions which studied the effect of supercritical carbonation concentration (0% and close to 100% of CO2), the effect of cellulosic pulp (unbleached or bleached), and durability. All samples were subjected to mechanical, physical, and microstructural tests. The initial period of thermal curing (varying from 24h to 48h) and exposure time to carbonation (from 1h to 2h), did not have a statistically significant effect on the mechanical performance of the composites. However, the flexural test results of carbonated composites reinforced with bleached pulp showed a statistically significant improvement when compared to unbleached pulp reinforcement (24% increased average modulus of rupture). Thus, for cementitious composites cured with supercritical carbonation, the use of bleached cellulosic pulp, 24h of thermal hydration and 1h in an environmental chamber provided the optimal curing conditions and the most desirable properties in this study.

Sinabung Volcanic Ash Utilization As The Additive for Paving Block Quality A and B

Paving block is one of the building materials used as the top layer of the road structure besides asphalt and concrete. Paving block is made of mixed materials such as portland cement or other adhesive materials, water and aggregate. In this research, the material used as the additive of cement and concrete is volcanic ash from Mount Sinabung, it is based on the results of the material testing, Sinabung ash contains 74.3% silica (SiO2). The purpose of this research aims to analyze the behavior of the paving blocks quality A and B with and without a mixture of Sinabung ash, to analyze the workability of fresh concrete using Sinabung ash as an additive in concrete, and to compare the test results of paving blocks with and without using Sinabung ash. The samples that we made consist of four variations of the concrete mix to experiment a mixture of normal sample without additive, samples which are mixed with the addition of Sinabung ash 5%, 10%, 15%, 20% and 25% of the volume of concrete/m3. Each variation consists of 10 samples of the concrete with 28 days curing time period. We will do the compressive strength and water absorption test to the samples to determine whether the samples are in accordance with the type needed. According to the test result, paving blocks with Sinabung ash and curing time reach quality A at 0%, 5% and 10% mixture with the compressive strength of each 50.14 MPa, 46.20 MPa and 1.49Mpa, and reach quality B at 15%, 20 %,25% mixture with curing time and 0%, 5%, 10%, 15%, 20% and 25% mixture without curing time. According to the absorption values we got from the test which are 6.66%, 6.73%, 6.88%, 7.03%, 7.09% and 7.16%, the entire sample have average absorption exceeding SNI standardization which is above 6% and reach quality C. Based on compressive strength and absorption data obtained Sinabung ash can’t fully replace cement as the binder because of the low CaO content.

Curing studies and mechanical properties of glass fiber reinforced composites based on silanized clay minerals

A commercial organically modified montmorillonite Cloisite® 15A was modified via a new silanization route by two different silane coupling agents: 3-Aminopropyltriethoxysilane and 3-Glycidyloxypropyltrimethoxysilane. This method enables the use of very high concentration of silanes for functionalization of clay minerals. The ratio of weight of silane coupling agent to that of weight of clay mineral (X) was varied from 0.1 to 6. Small angle X- ray scattering and thermogravimetric analysis were carried out on silane modified clay minerals to quantify the grafting of silanes as a function of ratio of weight of silane agent to that of clay mineral. Fiber reinforced epoxy nanocomposites containing silylated clay minerals were manufactured using vacuum assisted resin infusion molding method. Also, curing studies were carried out on fiber reinforced epoxy nanocomposites containing Cloisite® 15A at different cure temperatures, e.g. 70°C, 80°C, 85°C, 95°C and for two different curing time periods, e.g. 7h and 10h. Significant improvements in mechanical properties of fiber reinforced nanocomposites were obtained with incorporation of clay minerals silanized using high concentration of silanes in solvent and chosen curing schedule. The tensile modulus, tensile strength, flexural modulus and bending strength increased by 30%, 37%, 139% and 146% respectively, in nanocomposites containing clay mineral modified using 4X aminopropyltriethoxysilane. An attempt has been made to correlate the results with the morphology of nanocomposites by transmission electron microscopy and that of fractured surfaces by scanning electron microscopy.

A unique relationship determining strength of silty/clayey soils – Portland cement mixes

This technical note advances the understanding of the key parameters controlling the unconfined compressive strength (qu) of artificially cemented silty/clayey soils by considering distinct moisture contents, distinct specimen porosities (η), different Portland cement contents and various curing time periods. The qu values of the specimens moulded for each curing period were normalized (i.e. divided) by the qu attained by a specimen with a specific porosity/cement index. A unique relationship was found, establishing the relationship between strength for artificially cemented silty/clayey soils considering all porosities, Portland cement amounts, moisture contents and curing periods studied. From a practical viewpoint, this means that, at limit, carrying out only one unconfined compression test with a silty/clayey soil specimen, moulded with a specific Portland cement amount, a specific porosity and moisture content and cured for a given time period, allows the determination of a general relationship equation that controls the strength for an entire range of porosities and cement contents, reducing considerably the amount of moulded specimens and reducing projects development cost and time.

Behavior of Soil–Fly Ash–Lime Blends under Different Curing Temperatures

Compaction of layers of soil–fly ash–lime blends is often used to improve soil conditions for infrastructure projects. Such understanding is the starting point to develop more rational dosages that allow for a more efficient use of resources. To achieve this objective the present research aims to quantify the influence of curing temperature (T), amount of lime (L), porosity (η), and porosity/lime ratio (η/Liv) on the assessment of splitting tensile strength (qt) and unconfined compressive strength (qu) of sand–coal fly ash–lime blends. A series of splitting tensile and unconfined compression tests were carried out in the present work. The results show a linear function fits well the relation between qt and qu with L, and a power function fits well as the relation between qt and qu with η for all curing temperatures of the specimens. It was also shown that the porosity/lime ratio (η/Liv) is a good parameter in the evaluation of qt and qu of the studied blends for the whole range of lime, porosities and temperature studied, at specific amount of coal fly ash (25%) and curing time period (28 days). The volumetric cementitious material content (Liv) is adjusted by an exponent (0.30 for all curing temperatures blends) to end in unique correlations for each temperature. For the sand, coal fly ash, lime, curing time period and curing temperatures, a unique relationship was achieved linking qt as well qu to η; Liv and T. For a given curing time period (28 days), the relations qt-η/Liv and qu-η/Liv versus T are shown to vary linearly up to a threshold, when asymptotes occur. Finally, the relation between qt/qu is a constant and equal to 0.19 for the whole range of L, η and T studied.

Tensile Strength Properties of Sand-bentonite Mixtures Enhanced with Cement

Measurement of tensile strength of soil by direct methods can be challenging due to difficulties in sample preparation and in fixing the specimen while applying uniaxial tension forces. However the tensile strength of soil samples can be measured by indirect tests, such as the Brazilian and double punch tests, assuming that tensile stress is distributed uniformly on the failure plane. In this study, the tensile strength of statically-compacted sand bentonite and cement-enhanced sand bentonite mixtures is measured in varying curing time periods using the “double punch” test. The compressive strengths of samples are also measured using the unconfined compression test, and the correlation between tensile and compressive strength is discussed in relation to curing time. A simple method is also applied to determine the undrained cohesion and internal friction angle of samples through the Mohr-Coulomb circle method, using the double punch tensile strength and unconfined compressive strength. The results show that cohesion increases in both sand bentonite and sand bentonite-cement samples along with curing time.

Remediation of Expansive Soils Using Agricultural Waste Bagasse Ash

Bagasse is a fibrous material remaining after crushing sugarcane to extract its juice; and bagasse ash is produced after burning bagasse. Improper disposal of this material can create environmental problems around sugar manufacturing plants. Bagasse ash, comprising a high percentage of silica (SiO2), is considered as a sensible pozzolanic material with non-reactive behaviour and has potential to be used in road subgrade stabilisation. One of the main challenges for transportation organisations in Australia is to treat subgrades including expansive soils. Expansive soils exhibit significant movements when the moisture content changes, and hence it causes substantial damage to road pavements constructed over these type of soils. Road engineers need to employ materials having acceptable strength, relatively low price and being eco-friendly. In order to demonstrate the potential ability of bagasse ash in curtailing the adverse effects of expansive soils on roads, an array of experimental tests using bagasse ash have been conducted. In this study to activate and improve the effectiveness of bagasse ash, hydrated lime was used and mixed with black soil samples, collected from Queensland Australia. Samples were prepared using different contents of bagasse ash and hydrated lime (0%, 6%, 10%, 18% and 25% by the dry mass of soil), at a ratio of 3:1, respectively. The results of free swell ratio (FSR) test, unconfined compression strength (UCS) and California bearing ratio (CBR) tests are presented for untreated and treated samples after various curing time periods of 3, 7 and 28 days. The outcomes of these tests clearly demonstrate that stabilisation of expansive soils using bagasse ash and hydrated lime not only improves the strength, but also facilitates to cope with environmental concerns through reduction of sugar industry waste material.

Mohr–Coulomb failure envelopes of lime-treated soils

The aim of this study is to quantify the influence of amount of lime and porosity in the assessment of the Mohr–Coulomb failure envelope of lime-treated soils based on unconfined compressive strength (σc) and splitting tensile strength (σt) of such materials, without the necessity of carrying out triaxial testing. Based on a previously established concept that the σt/σc relationship is unique for each specific fine-grained soil and lime blend, it is shown that the effective angle of shearing resistance of a given lime-treated soil is independent of the porosity and the amount of lime of the specimen and that effective cohesion intercept is a direct function of σc (or σt) of the improved soil; this in turn depends on the porosity and volumetric amount of lime in the soil–lime blends. Finally, the concepts are successfully tested for clayey sand treated with lime at two distinct curing time periods, considering weak to moderate cementation levels.

The UV and Laser Aging for PMMA/BDK/Azo-dye Polymer Blend Cured by UV Light Beams

A polymeric-based solution blend composed of Azo-dye methyl red (MR) doped with polymethelmethacrelate (PMMA) solution, in addition, to the BenzylDimethylKetal (BDK) photoinitiator was made with optimum molar ratios and deposited on glass substrate by spin coating technique. The samples were then exposed to UV light beams in order to assist the layers polymerization by the proper exposure process. The photo chemical reaction occurred during the UV light polymerization process induces photo refractive changes which were presented as a function of wavelength or photon energy. Two main strong absorption peaks were observed in the films at around 330 nm (3.75 eV) and 500 nm (2.48 eV) for different curing time periods. This phenomenon enhances the films usage for optical data storage media at these two wavelengths. Since the deposited films were then useful as based layers for Read/Write optical data storage media, they were then tested by UV or laser Read/Write beams independently. The optical properties of the films were investigated while exposed to each beam. Finally, their optical properties were investigated as a function of aging time in order to relate the temporary and/or permanent light-exposure effect on the films compared to their optical properties before the light exposure. The films show a low absorbance at 630 nm (1.97 eV) and high absorbance at 480 nm (2.58 eV). This fact makes it possible to record holographic gratings in the polymeric film upon light exposure. In all cases the optical properties were evaluated by using the very sensitive, non destructive surface testing spectroscopic ellipsometry technique. The films were characterized in the spectral range of 300 to 1000 nm using Lorentz oscillator model with one oscillator centred at 4.15 eV. This study has been supported by the SEM and EDAX results to investigate the effect of the UV and visible beams on their optical properties. The results of this research determined the proper conditions for depositing the proper optical materials for light sensors or Read/Write optical data storage media for the UV or the laser Read/Write heads.

A testing procedure for predicting strength in artificially cemented soft soils

It is globally recognized that soft soils will have low strength and high compressibility and that under reduced loads might collapse or suffer large displacements. In order to reduce settlements and increase bearing capacity of structures built on such soils, their stabilization using cementitious materials such as Portland cement and/or quicklime (increasing strength and stiffness) is an efficient technique used worldwide. The focus of this research is to present and check the accuracy of a new testing procedure to evaluate strength gain in very soft soils when using cementation as a means of improvement. This testing procedure was intended to fasten acquiring strength results in artificially cemented soft soils. In short, in the proposed procedure the force applied to embed a flat base rod into a soil mass is measured by using high resolution load rings. The proposed flat base rod embedding test was shown to be adequate for evaluating the gain in strength of cemented soils. Results of embedding flat base rod strength have unique linear relations with both unconfined compressive strength and splitting tensile strength, being independent of type and amount of cementitious material (Portland cement and/or quicklime), as well as of the curing time period. The wrap up of present studies is that the developed testing procedure can be used as a substitute of unconfined compression and splitting tensile tests as a dosage test, being easier to mold specimens (might be molded in the field) and faster in acquiring strength results (can be carried out in a bucket filled with soil and the cementitious material, in which will be attached to the load ring) in artificially cemented soft soils.

In Vitro and In Situ Fiber Bragg Grating Sensor Analysis of Two Dental Resin Cements

This study evaluated the shrinkage polymerization of two dual-curing resin cements during in vitro and in situ tests, using fiber Bragg grating with different curing time periods. The cements used were: Relyx ARC (dual conventional) and Relyx U200 (dual self-adhesive). For the in vitro experiment, the resin cements and the sensors were placed between two glass coverslips and afterwards were photoactivated for 40 s ( N = 20). For the in situ experiments, 20 human teeth were prepared to receive root posts cemented with the same two resin cements. Two sensors were glued to the posts’ surfaces at the coronal and apical thirds. Next, the cementation of the posts was photoactivated for 40 s. The sensors measured the strain for 60 min in both experiments. Data from in vitro and in situ experiments were analyzed by three-way ANOVA and Games–Howell multiple comparison procedures. Data from the coronal and apical thirds were analyzed by two-way ANOVA and T-test. The results showed that the polymerization shrinkage values are similar for the in vitro and in situ experiments, that contraction is greater after 5 minutes curing time compared to the contraction at 60 min, that both resin cements performed similarly and that the shrinkage measurement at the cervical third showed higher values than those at the apical third.

Assessing Failure Envelopes of Soil–Fly Ash–Lime Blends

AbstractThis study aims to establish the influence of curing time and the amount of lime and porosity in the assessment of the Mohr-Coulomb failure envelope of fly ash–lime-treated soils based on unconfined compressive strength (σc) and splitting tensile strength (σt) of such materials. Founded on the concept that the σt/σc relationship is unique for each specific fine-grained soil, fly ash, and lime blends, it is shown that the angle of shearing resistance of a given lime-treated soil is independent of the porosity and the amount of lime of the specimen and that cohesion intercept is a direct function of σc (or σt) of the improved soil, which depends of the porosity and volumetric amount of lime of the soil–fly ash–lime blends. Finally, the concepts are tested with success for a sandy soil treated with fly ash and lime at distinct curing time periods, considering moderate to strong cementation levels.

Preparation and Optimization of Poly(Vinyl Formal) from Poly(Vinyl Acetate) for Electrical Insulation

The preparation of poly(vinyl formal) suitably used for wire insulation from commercially available local substances was investigated in this study. Such resin was prepared with higher formal content up to 82.3% from poly(vinyl acetate), acetic acid, and formaldehyde by solution polymerization technique which consists of hydrolysis of poly(vinyl acetate) to poly(vinyl alcohol) and this subsequently convened by formalization to poly(vinyl formal) at 70°C and reaction time of 24 hours. The three grades are 29, 35, and 50% of poly(vinyl acetate) have been investigated, only poly(vinyl acetate) with 29% solid yields a polymer nearest to that reported in the literature, also different amount of glacial acetic acid were used. Hydrolysis reaction seems highly enhanced by the presence of glacial acetic acid as solvent. The prepared poly(vinyl formal) was mixed with resole phenolic resin to produce coating and improve the mechanical, electrical, and thermal properties of the poly(vinyl formal). Different concentrations, temperatures, and curing time periods and were examined to find the optimum conditions: concentration of 10wt% resole phenolic resin, 162 o C curing temperature, and 30 min curing time.