Reduction In Compressive Strength Research Articles

Potential uses of different sustainable concrete mixtures in gamma and neutrons shielding purposes

Gamma and neutron radiation causes severe effects on human health; many nuclear accidents led to radiation leakage affecting the environment and human health during the last century. Therefore, a great need for radiation shielding is now in demand. Concrete is the main constituent in any shielding design. This research investigates the mechanical properties of traditional concrete mixtures incorporating ilmenite or tourmaline aggregates. The crushing value of tested aggregates, along with the compressive and tensile behavior of concrete samples, was evaluated. Test results showed a general reduction in compressive and tensile strength of ilmenite concrete compared to conventional concrete by up to 18.2% and 27.5%, respectively.In contrast, tourmaline concrete achieved superior compressive and tensile strength than its conventional counterpart by up to 26.23% and 23.79%, respectively. The new concrete samples (Ilmenite and Tourmaline) are used in gamma and neutrons emission attenuation. Results show high gamma attenuation for both ilmenite (23–73%) and Tourmaline (32–79%). As for neutrons, the attenuation when using ilmenite was (9–37%) and for Tourmaline (13–42%).

A Two-Step FE Model Updating Approach for System and Damage Identification of Prestressed Bridge Girders

This study presents a two-step FE model updating approach for health monitoring and damage identification of prestressed concrete girder bridges. To reduce the effects of modeling error in the model updating process, in the first step, modal-based model updating is used to estimate linear model parameters mainly related to the stiffness of boundary conditions and material properties. In the second step, a time-domain model updating is carried out using acceleration data to refine parameters accounting for the nonlinear response behavior of the bridge. In this step, boundary conditions are fixed at their final estimates using modal-based model updating. To prevent the convergence of updating algorithm to local solutions, the initial estimates for nonlinear material properties are selected based on the first-step model updating results. To validate the applicability of the two-step FE model updating approach, a series of forced-vibration experiments are designed and carried out on a pair of full-scale decommissioned and deteriorated prestressed bridge I-girders. In the first step, parameters related to boundary conditions, including stiffness of supports and coupling beams, as well as material properties, including initial stiffness of concrete material, are estimated. In the second step, concrete compressive strength and damping properties are updated. The final estimates of the concrete compressive strength are used to infer the extent of damage in the girders. The obtained results agree with the literature regarding the extent of reduction in concrete compressive strength in deteriorated concrete structures.

Cow dung ash (CDA): A sustainable conductive filler for enhancing electromagnetic shielding property of cement mortar

Cow Dung ash (CDA) is a wide spread farm by-product, generated by burning dry cow-dung. Cement mortar, the work horse of construction industry inherently possesses significant electrical conductivity, thereby providing considerable electromagnetic shielding property. CDA is investigated as novel sustainable conductive filler, as sand replacement, for enhancing electromagnetic shielding property of cement mortar. The electromagnetic properties of CDA are determined employing standard wave guide techniques, in X band, and electrical conductivity around 10-2 S/m is observed. The electrical loss tangent is observed around 0.2–0.3. Cement mortar slabs with CDA as sand replacement are prototyped. Sand replacement till 15 % by volume is investigated. Considerable reduction in compressive strength is reported in literature for sand replacement beyond 15 %. After 28 days of curing, the prototyped slabs are subjected to electromagnetic shielding effectiveness determination, as per ASTM 4935 two antenna standard, in the X band of frequencies centred around 10 GHz. Shielding Effectiveness (SE) around 7 dB is observed for 3 % CDA as sand replacement, around 10 dB for 10 % replacement, and around 20 dB for 15 % CDA. Compressive strength measurement employing Universal Testing machine presented significant reduction in compressive strength as CDA replacement tend towards 15 %. Employing CDA loaded cement mortar for plastering, is a low cost, easy deployable solution for realizing customized electromagnetic shielding levels in buildings housing critical electrical and electronic infrastructure including servers and data centres. Realizing low cost, easy deployable customized shielding solutions is an upcoming research domain, primarily due to the anticipated increase in ambient electromagnetic field levels in our surroundings caused by the rampant deployment of communication technologies including 5G and IoT. Apart from providing positive environmental impact, acting as sand replacement, enhanced CDA utilization by engineering sectors can lead to good revenue generation model for rural economic development.

Development of Eco-friendly Self-compacting Concrete Using Fly Ash and Waste Polyethylene Terephthalate Bottle Fiber

This study aims to utilize fly ash and waste PET bottles for producing more sustainable self-compacting concrete (SCC) with better mechanical strength. Fly ash is utilized as a supplementary cement material and waste PET bottles as fiber reinforcement to improve its flexural strength and achieve the targeted compressive strength. The experimental works were conducted on eight variations using 80 specimens, divided into two main groups of partial cement replacement using 0% and 15% fly ash by weight. The two variants are added with PET fiber based on the volume fractions of 0%, 0.25%, 0.50%, and 0.75%. Fresh concrete was tested using the slump flow method (T50) and the Visual Stability Index (VSI) based on ASTM 1611. The hardened concrete tests are conducted after 56 days and include testing the concrete's compressive strength, flexural strength, and ultrasonic pulse velocity. Test results showed that the presence of PET fiber in the SCC mix decreased its flowability. However, when added up to 0.75%, the mixes still meet the flowability requirements of fresh-state SCC. PET fiber addition tends to reduce the compressive strength, whereas the reduction in compressive strength of SCC with PET fiber without fly ash is insignificant. However, in SCC that uses fly ash, the addition of PET fiber causes a significant decrease in its compressive strength. Adding PET fiber into SCC mixes can increase flexural strength, both for the two variants: SCC without fly ash and SCC with fly ash. It can be concluded that PET waste fiber with an aspect ratio of 40 can be added up to 0.5% for SCC without fly ash and up to 0.25% by volume fraction for SCC with fly ash addition. The ultrasonic pulse velocity test results have an excellent tendency to predict the concrete's compressive and flexural strengths. Therefore, the UPV test can be applied for the non-destructive test evaluation of PET fiber-reinforced SCC. Doi: 10.28991/CEJ-2023-09-02-014 Full Text: PDF

Novel resource utilization approach of spent catalyst from flue gas denitrification: Preparing high quality titanium-bearing pellets

Spent titanium-based catalyst is a waste generated by the selective catalytic reduction (SCR) denitrification process, whose generation is dramatically increasing in the iron and steel industry year by year. A novel approach was proposed in this work to prepare titanium-bearing pellets by using spent catalyst. The influences of spent catalyst addition on the comprehensive properties of pellets were studied. The corresponding relationship between the change of phase structure and the spent catalyst pellets' strength was investigated. The results demonstrated that the spent catalyst could be adsorbed on the surface of ore particles physically and chemically, improving the adhesion of particles inside the pellet and the hydrophilicity, thus obtaining good comprehensive performance of the green pellets. When adding 5.0 wt% spent catalyst, the bentonite dosage could be reduced by 50%, and the strength of roasted pellets could meet the requirement of large blast furnaces. The consolidation mechanism of the spent catalyst pellets indicated that TiO2 reacted with FeO first to generate FeTiO3 in the preheating process and further oxidized to form Fe2TiO5 in the roasting process. The unreacted TiO2 would appear in the roasted pellets and inhibit recrystallization and polycrystalline growth of Fe2O3 grains, resulting in the reduction of compressive strength. Overall, high-quality titanium-bearing pellets could be obtained when the amount of spent catalyst was less than 5.0 wt%. This study thus provided an alternative route to resource utilization of spent catalysts in iron and steel enterprises.

Influence of expansive cement on rheological, strength performance and morphological characteristics of self-compacting concrete

This research is focused on the influence of type K expansive cement (calcium sulfoaluminate-belite cement) blended with self-compacting concrete (SCC) in the presence of alccofine and silica fume. The present work intends to evaluate the synergistic effect of expansive cement in various proportions from 0 to 15 % by cement weight by examining the rheological properties, mechanical strength and expansive characteristics for M30, M40 and M50 grades of SCC. Results revealed that the incorporation of expansive cement is constructive in improving fresh state properties, mechanical performance and reducing shrinkage properties effectively due to the formation of additional ettringite and calcium hydroxide. Results of fresh properties of expansive SCC show a good agreement with European standards. The test results illustrate a positive influence on strength properties of SCC at the early age with the inclusion of 10 % of expansive cement due to the formation of additional ettringite and calcium hydroxide. Incorporating 10 % of expansive cement enhanced the compressive strength by 12 %, 9% and 7 % for M30.M40 and M50 grades of SCC respectively relative to reference SCC at 28 days. However, a slight strength reduction in compressive strength is noticed for SCC with the inclusion of higher percentage (15 %) of expansive cement. The effect of expansive cement on the morphological characteristics of SCC was assessed by employing SEM, EDS, XRD and FTIR techniques to validate the experimental results. On the other hand, addition of expansive cement and supplementary cementitious materials in the production of SCC minimizes the use of Portland cement and significantly reduces carbon footprint.

Performance of Rubberized Concrete and the Effect of Temperature and Stainless Steel Fibers

Rubberized concrete is widely used in construction by utilizing the advantages of partially replacing fine or coarse aggregate with rubber to enhance several properties of concrete and provide an environmentally friendly solution. This paper experimentally explores the influence of utilizing crumb rubber (CR) as an alternate coarse aggregate in concrete. Concrete specimens were prepared with different percentages of rubber (0%, 5%, 10%, 15%, and 20%). Additionally, other parameters, such as freezing–thawing cycles, temperature, and stainless steel fibers (SSFs), were investigated. The workability of fresh concrete and the compression properties of hardened concrete were examined. Reductions in the mechanical properties of rubberized concrete were obtained. The compressive strength reductions ranged between 13% and 50%, based on the percentage of CR in the concrete mix. However, a lesser unit weight and higher toughness were obtained relative to conventional concrete. The average unit weight decreased by 1.3%, 2.5%, 3.4%, and 5.7% of the control mixture when 5%, 10%, 15%, and 20% of the CR were incorporated into the concrete mixtures, respectively. Regression models to predict the compressive strength and unit weight of concrete with CR were developed. In addition, a life cycle cost analysis (LCCA) to identify and quantify the possible benefits of using CR in concrete mixes was carried out. Using rubberized concrete mixtures for thin whitetopping offered a slightly lower net present value compared to the ordinary concrete mix.

Influence of macro-synthetic fiber on the mechanical properties of iron ore tailing concrete

Iron ore tailing (IOT) is a hazardous by-product of iron extraction, and its disposal has resulted in serious environmental issues. This paper investigated the interfacial bond performance of macro-synthetic fiber (MSF). The effect of the IOT replacement ratio on the compressive performance of concrete and the effects of MSF on the compressive and flexural performance of IOT concrete were evaluated. Test parameters included IOT replacement ratio (0%, 50% and 100%), fiber volume fraction (0%, 0.5%, 1.0%, 1.5% and 2%) and fiber aspect ratio (43, 60 and 69). The test results indicated that the deterioration in compressive strength was observed with the increase in the IOT replacement ratio. The mechanism of the effect of IOT on the compressive performance of concrete was analyzed. However, the incorporation of MSF compensated for the reduction in compressive strength caused by iron ore tailings (IOTs). Furthermore, the post-cracking performance, which includes residual flexural tensile strength, equivalent flexural tensile strength and fracture energy, of concrete increased with the increase in fiber volume fraction. The fracture energy of IOT concrete increased by a factor of 18.06–20.19, and the post-cracking performance of IOT concrete was comparable with that of natural sand (NS) concrete at an MSF fiber volume fraction of 2%. At a given fiber volume fraction, the MSF with a higher fiber aspect ratio was more effective in improving post-cracking performance than one with a lower aspect ratio. Moreover, new empirical equations were proposed, which can accurately predict the residual flexural tensile strengths and equivalent flexural tensile strengths. These results provide important implications for determining the contribution of MSF in strengthening and toughening IOT concrete.

Feasibility study of dealuminated kaolin utilization in marine constructions

In the marine environment, the resistance of cement structures to salts is the most critical factor affecting their life span. We investigated the sulfate attack of ordinary Portland cement (OPC) and dealuminated kaolin (DK) blended cement in the marine environment. The performance of this cement was assessed by immersing the mortar specimens in fresh seawater for one year and measuring the strength development, reduction in compressive strength, expansion due to (SO42-) penetration, and weight change of the mortar specimens using the standard test methods. The results proved clearly that 7.5% (DK) blended cement mortar specimen is the best achieved the lowest reduction in compressive strength (10%), a relatively small weight gain (0.62%), and expanded to less than 0.10% at 1-year exposure so it is considered sulfate resistant.

Behaviour of engineered cementitious composite (ECC) with utilization of waste materials: A review

Engineered Cementitious Composite (ECC) is a special type of composite with high ductility, tensile strength and pseudo-hardening behaviour. The design of Engineered cementitious composite is based on micro mechanics concept with 2% volume fraction of polyvinyl chloride (PVC) fibres. To reduce the cost, constituents of ECC were replaced with locally available material or waste material and effect of these replacements on its mechanical properties was studied by different researchers. A review study was carried on previous research studies to summarize the effect of replacements of different constituents of ECC on the mechanical properties of ECC. In this research paper the effect of replacement of cement with limestone calcined clay cement (LC3), glass powder (GP), ceramic polishing brick powder (CPBP) etc. and fine aggregate with limestone powder, geo-polymer aggregate, M-Sand, crumb rubber, quartz sand etc. has been explored. Partial replacement with post-processed sugar bagasse ash and fly ash led to reductions in compressive strength. Incorporation of glass powder, ceramic polishing brick powder (CPBP), slag, and nano silica showed varying effects on strength and strain capacity of ECC. Replacing fine silica sand in ECC with coarse river sand maintained compressive strength and tensile strain but decreased tensile strength, while limestone powder increased early-age compressive strength but decreased long-term strength in high volume fly ash ECC. Using waste material as a replacement for cement has reduced the amount of cement used in ECC, which reduces carbon and energy footprints, making ECC green and cost effective.

Applicability of cementitious capsules in concrete production: initial assessment on capsule robustness, mechanical and self-sealing properties of concrete

The use of macrocapsules in self-healing applications offers a potential benefit by carrying a larger amount of healing agent in comparison with microcapsules. However, the application of macrocapsules is still limited to paste and mortar levels on lab-scale. This is due to a concern that most capsules might be broken when mixed with concrete components. In this study, cementitious tubular capsules were used and they were considered as a partial replacement of coarse aggregates (2 vol% gravel). The capsules have a dimension of 54 mm and 9 mm in length and outer diameter, respectively. A water-repellent agent (WRA) was entrapped in the capsules as a proposed agent to seal the crack. Initial results revealed high survivability of capsules during concrete mixing: 100% survival ratio when tested in a drum mixer and 70–95% when tested in a planetary mixer. The mechanical and self-sealing properties of concrete containing embedded capsules were evaluated. With the addition of capsules, around 8% reduction of compressive strength was noticed, but no further effect on splitting tensile strength was detected as compared with concrete without capsules. Ultrasonic pulse velocity (UPV) tests confirmed that the presence of capsules also did not significantly affect the compactness of the hardened concrete. Furthermore, the embedded capsules were able to break when a crack was introduced and it was found that 90% sealing efficiency was achieved by capsule-based concrete as a result of the successful release of sealing agent into the crack.

Investigation of Mechanical Properties of M-sand concrete with Polypropylene and Steel fibers

This study looks into the impact of the adding of polypropylene(pp) and Hooked-end steel (HES) fibre on the mechanical characteristics of M-sand concrete (MSC). HES fibres with a 30-mm length were used at 1% to the weight of the cement for every mix and Polypropylene(pp) fibers with length 12-mm were used at the content of 0.25%, 0.50%, and 0.75% and 1%. All the mixes were produced with the mixing of HES and pp fibers. All the mixes with fiber-reinforced concretes (FRC) contained 60% M-sand as fine aggregate (FA) replacement. For increment of workability, the super plasticizer is also added. The compressive strength, splitting tensile strength, flexural strength of the concrete mixes was examined for M30 Concrete. Results of this work indicated that the adding of the M-sand improves compression characteristics of plain concrete mix. The outcomes also show that the mechanical characteristics of MSC were amplified by the addition of steel (HES) and polypropylene (pp) fibers at each weight fraction taken into account in this investigation. Additionally, it was found that adding 1% steel fiber considerably increased the concrete’s split tensile test values and also flexural test values. The blend with the highest performance out of all the varied steel and polypropylene(pp) fibre combinations tested had 1% HES and 0.5% pp fiber. Finally, the findings demonstrated that adding fibres to concrete led to reduction in compressive strength and increase in the value of split tensile strength and also flexural strength.

Experimental investigation of the effect of thermal cycling on the thermomechanical properties of three rock varieties for high temperature thermal energy storage

During the past years “rock batteries” have become increasingly relevant for the storage of renewable energy sources, such as wind and solar energy, because of their economic and ecological advantages with respect to previously more common materials for thermal energy storage (TES) such as salt. In rock-based TES systems, thermal energy is stored in packed-bed rock using air as heat transfer fluid. We investigated three different rock types with respect to changes in thermomechanical properties after different numbers of thermal cycles, Ruhr sandstone (Oberste quarry in Dortmund - Germany), basalt (commercial MTV basalt) and Calanca gneiss. Cylindrical samples were heated to 800°C within 11,5 h before temperature was kept constant for another 30 min and then decreased within 11,5 h. Samples were thermomechanically investigated before thermal treatment, and again after 1, 3, 7 and 15 cycles. Additionally, two samples of each rock type were subjected to a thermal cycle with a maximum temperature of 450°C and to 1000°C, respectively, at a heating/cooling rate corresponding to that of the samples heated to 800°C. Samples were characterised with respect to ultrasound wave velocity, bulk density, thermal conductivity, thermal diffusivity, uniaxial compressive strength, splitting tensile strength, mineral content (X-ray powder diffraction) and microstructure (thin section analysis). Samples of basalt could not withstand the standard heating rate. The samples crushed into small pieces also when heating rates were reduced and at a maximum heating temperature of 800°C. For sandstone and gneiss, the ultrasound wave velocity, bulk density, thermal conductivity, thermal diffusivity, uniaxial compressive strength and splitting tensile strength decreased systematically with increasing number of cycles, while the maximum reduction occurred after the first cycle and the relative reduction was similar between both rocks. Microstructural analysis indicated an increase in crack density and minor mineralogical changes upon heating. Both rocks, Ruhr sandstone and Calanca gneiss, appear suitable for TES, but Calanca gneiss is less suitable for temperatures above 800°C due to a significant reduction in bulk density and uniaxial compressive strength when heated to 1000°C. Also, its anisotropy and anisotropic response to heating can lead to preferred flow paths of the heat transfer fluid. Ruhr sandstone maintains a high uniaxial compressive strength of about 100 MPa even after 15 cycles while thermal capacity was only slightly reduced or even increased, and can be recommended for use in high temperature TES. This study is the outcome of a research-oriented teaching program at Ruhr-University Bochum within the Geoscience curriculum for students with focus on Engineering Geology. Student authors (Fränzer to Thomas) are listed in alphabetical order.

Experimental study on the preparation of magnesium oxysulfate cement-based composites using waste locust powders to replace non-renewable magnesium oxide

Magnesium oxysulfate cement is a new type of environment-friendly cement with low energy consumption and promising development potential. But the raw material MgO is not renewable. To improve the utilization of forestry wastes and save MgO, composites containing locust powders with 0 ∼ 25 % mass of MgO were prepared by mechanical mixing and curing for 3d ∼ 100d. The slurry’s fluidity, mechanical property, water resistance and microstructure were studied. Strength data at 100d were found to be essential for property evaluation. The maximum locust dosage based on fluidity was 25 %, and composites with 10 %∼25 % locust exhibited flexural strength of 13.37 ∼ 15.12 MPa and compressive strength of 56 ∼ 64.3 MPa at 100d. The corresponding flexural strength improvement and compressive strength reduction comparing to cement with no locust were by 13.5 %∼28.35 %, and 21.86 %∼31.95 %, respectively. Regarding relations of flexural force and displacement before fracture at 100d, locust with 10 %∼25 % dosage improved the displacement and energy absorption capacity by 56.88 %∼125.58 % and 52.48 %∼108.49 %, showing lower brittleness. Composites containing 10 %∼25 % locust improved the flexural strength by 14.23 %∼48.82 % when soaking in water, and the softening coefficient was larger than 0.85 if cured for 35d and soaked for 7d, indicating good water resistance. Effects of locust dosage on primary functional groups, phase changes, thermal stability and microstructure were analyzed by various techniques. A new optimization method based on seven indicators is proposed, capturing the optimal locust dosage as 20 % mass of MgO. This paper proposed an environmental-friendly approach to improve the utilization of forestry wastes and develop new cement-based building materials.

Short-Time Effects on Compressive Strength of Residual Soils Due to Rainwater

Abstract: The short-term effects of acid rain on the geotechnical properties of residual soil were investigated. Artificial acid rain (AAR) of pH values 2, 4 and 6 was created with an infiltration setup to replicate the interaction between acid rain and soil. The soil specimens were infiltrated with AAR for durations of 30mins and 60mins for each pH level of 2, 4 and 6 and a control sample using deionised water of pH 7.5. Unconfined compression test (UCS) and Atterberg limits test were performed on the treated samples to study the mechanical behaviour and the characteristics of the soil once contaminated with AAR. The results revealed that reducing the pH value of AAR led to a reduction in compressive strength and Young’s modulus and an increment in liquid limit while the plastic limit remained unchanged. The reduction in compressive strength due to acid rain was observed to be almost halved when the bulk unit weight of the soil was increased for the same infiltration period.

Consolidation and reduction behaviour of pellets with sea sand vanadium titanomagnetite: a microscopic interpretation of macroscopic properties

ABSTRACT The compressive strength of pellets is of great significance for the evaluation of pellets quality indexes. In this paper, the chemical composition, mineral phase composition and microstructure of pellets were analyzed by ICPAES, XRD, OM and SEM-EDS through oxidation roasting and gas-based reduction experiments. The effect mechanism of thermal regulation on the compressive strength and reduction performance of pellets was explained by the micro-indicators such as porosity, Vickers hardness and morphological structure of pellets. The results showed that with the increase of the roasting temperature and the extension of the roasting time, the internal porosity of the oxidized pellets was reduced, while the compressive strength of the pellets was continuously improved, and the roasting temperature had a greater influence on the compressive strength. However, the increase in porosity of the reduced pellets weakened the intergranular bonding between the particles, which led to a reduction in compressive strength.

Thermal Characterizations of Waste Cardboard Kraft Fibres in the Context of Their Use as a Partial Cement Substitute within Concrete Composites.

The building and construction industry consumes a significant amount of virgin resources and minimizing the demand with alternative waste materials can provide a contemporary solution. In this study, thermal components of kraft fibres (KFs) derived from waste cardboard are investigated. The mechanical properties containing KFs within concrete composites are evaluated. Metakaolin (MK) and KFs were integrated into concrete samples as a partial substitute for cement. Silica Fume (SF) was applied to the KF (SFKFs) with a view to enhancing the fibre durability. The results indicated that there was a reduction in compressive strength of 44 and 56% when 10% raw and modified KFs were integrated, respectively. Raw, fibre and matrix-modified samples demonstrated a 35, 4 and 24% flexural strength reduction, respectively; however, the tensile strength improved by 8% when the matrix was modified using MK and SFKF. The morphology of the fibres was illustrated using a scanning electron microscope (SEM), with an energy dispersion X-ray spectroscopy (EDS) provision and Fourier transform infrared spectroscopy (FT-IR) employed to gain insights into their chemical nature. The thermal, calorimetric and combustion attributes of the fibres were measured using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and pyrolysis combustion flow calorimetry (PCFC). SFKFs showed a lower heat release capacity (HRC), demonstrating a lower combustion propensity compared to raw KFs. Furthermore, the 45% decreased peak heat release rate (pHRR) of SFKFs highlighted the overall reduction in the fire hazards associated with these materials. TGA results also confirmed a lower mass weight loss of SFKFs at elevated temperatures, thus corroborating the results from the PCFC runs.

Utilization of Sodium Hydroxide (Naoh) to Treat Used Tyres as Sand Partial Replacement in Engineered Cementitious Composites

Engineered cementitious composites (ECC) is distinct for the tensile strain-hardening behaviourand tensile ductility contrasting to the quasi-brittle nature of ordinary concrete. The blended materials of ECC only consist of cement, sand, water, fibre, and admixture. The depleting and limited resources of sand in many countries have led to the research on alternative materials to replace sand partially or fully in the concrete mixture. Therefore, this study aims to utilize the crumb rubber (CR) in ECC as a partial sand replacement to enhance the ductility and energy dissipation capacity of the composite. The additional of CR in the ECC cause reduction of compressive strength of the composites due to its smooth surface resulting to less bonding with cement matrix. Hence, the CR is being treated with 10% sodium hydroxide (NaOH) to improve its surface roughness and enhance the adhesion between CR and cement matrix in the composites. The compressive strength results for ECC contained CR treated for duration of 2 days and 4 days were recorded. Two days is the optimum duration of CR treatment using 10% sodium hydroxide (NaOH) to lessen the reduction of the compressive strength of the rubberized engineered cementitious composites (R-ECC).

Combined Effect of Latex and Crumb Rubber on Mechanical Properties of Concrete for Railway Application

Crumb rubber incorporation is widely deemed to deteriorate the compressive strength of concrete. One of the dominant reasons for this strength reduction is known as the inferior bonding or weak interfacial transition zones (ITZ) between the crumb rubber and hardened cement paste. While Styrene-butadiene (SBR)latex is being used as a bonding agent in concrete manufacturing, the SBR latex usage holds the potential to compensate for the strength reduction from crumb rubber incorporation. This study focuses on evaluating the sole and combined effect of crumb rubber and SBR latex on the compressive strength, one optimum combination of latex modified rubberised mix (LMCRC) that had achieved 55.5 MPa of 28 days’characteristic strength was chosen to compare its impact resistance and stress-strain response to a plain concrete (PC) with similar characteristic strength. Experimental results showed both crumb rubber and SBR latex incorporation induced a compressive strength reduction in the concrete. The optimum latex modified rubberised mix with w/c of 0.32, crumb rubber replacement of 20kg/m3, and 3% latex additives had outperformed the control mix with w/c ratio of 0.38 by 66.7% and 293% in the 400mm span impact test and 200mm span impact test, respectively. Besides, the latex modified rubberised mix showed higher Poisson’s ratio, and higher compressive strain which indicates more ductile behaviour as compared to the plain concrete.

An Experimental Study on the Healing Performance of Complex Capsules Using Multiphase Inorganic Materials for Crack Self-Healing of Cement Mortars.

Recently, a self-healing technique capable of repairing cracks in structures has emerged. Among various self-healing technologies, self-healing capsules can be largely classified into two types, depending on the phase of the core material: solid capsules, in which the core material is a powder; and microcapsules, in which the core material is a liquid. Solid capsules and microcapsules have different mechanisms, and their capsule sizes are also distinctly different. This suggests that each has advantages and disadvantages. Most of the studies known to date have utilized single capsules. However, if one uses a mixture of the two types of capsules, it is possible to highlight the strengths of each capsule and compensate for the weaknesses. Therefore, in this study, the first research on complex capsules that mixed solid capsules and microcapsules was attempted. As a result of the experiment, the complex capsule slightly reduced the fluidity of the mortar, but the effect was not significant. Moreover, the complex capsule tended to reduce the compressive strength of the mortar. In particular, it was found that the effect of solid capsules on the reduction in compressive strength among complex capsules was greater than that of microcapsules. Conversely, the healing performance increased when the ratio of solid capsules in the complex capsules was large.