ASTM C1202 Research Articles

Alkali–Silica Reactivity Potential of Reactive and Non-Reactive Aggregates under Various Exposure Conditions for Sustainable Construction

The alkali–silica reaction (ASR) is a primary cause for premature concrete degradation. An accelerated mortar bar test is often used to access the detrimental phenomena in concrete caused by the ASR of aggregates. However, this test requires a certain environmental conditioning as per ASTM C1260. The objective of this study is to explore the effects of the cement alkali content, exposure solution concentration, temperature, and test duration on mortar bar expansion. Factorial experimental design and analysis was conducted to delineate the effects of the individual factors as well as their interaction. Five different aggregates with various mineralogical properties were used, representing reactive and non-reactive aggregates. Various dosages of cement alkalis (0.40, 0.80, and 1.20 Na2Oe), sodium hydroxide (NaOH) solution concentrations (0.5, 1.0, and 1.5 N), and temperature (40 °C, 80 °C, and 100 °C) were the studied variables. Mortar bar expansion was measured at 3, 7, 14, 21, 28, 56, and 90 days. Mortar bars incorporating Jhelum aggregates incurred expansion of 0.32% at 28 days, proving to be reactive aggregates as per ASTM C1260. Similarly, specimens incorporating Taxila aggregates showed expansion of 0.10% at 28 days, indicating non-reactive nature. It was observed that specimens with Sargodha aggregates showed expansion of 0.27% at 28 days for 0.50 N NaOH solution concentration compared to 0.31% expansion for identical specimens exposed to 1.5 N solution. Moreover, expansion increased with exposure duration for all the tested specimens. Experimental results showed that the cement alkali contents had relatively lesser effect on expansion for 1.0 N NaOH; while, in the case of 0.5 N and 1.5 N NaOH, the cement alkali had a significant effect. It was noted that expansion increased with an increase in the temperature. Jhelum aggregates showed 28-day expansion of 0.290% when exposed to 40 °C, but at a temperature of 100 °C, expansion increased to 0.339%. Factorial analysis revealed that the exposure solution had a major contribution towards the expansion of mortar bar specimens. This study highlights the contribution of various exposure conditions on the ASR expansion, which leads to a decisive role in selecting the aggregate sources for various applications and exposure conditions leading to sustainable construction.

Preventive Measures of Alkali–Silica Reaction in Concrete Buildings: Use of Hybrid Waste Coal Ash and Steel Wire Cut Fibers

The main cause of premature deterioration in concrete buildings is linked with the alkali–silica reaction (ASR) owing to the use of reactive aggregates and severe exposure conditions. This research aimed to explore the mitigation of ASR in concrete buildings using waste coal ash (CA) and steel fibers cut from long wire. CA and SF were acquired from a local market. The studied dosages of CA were 10%, 20%, 30% and 40% by cement weight and steel fibers were added at 0.5% and 1% of the total volume of the mixture. Specimens were cast and immersed in a 1N NaOH solution at 80 °C for 90 days as per ASTM C1260 guidelines. The compressive and flexural strengths of the control mixture without CA and the mixture with 10% of CA had a comparable behavior. A decrease in the compressive and flexural strengths was observed for higher dosages of CA (30% and 40%). Specimens incorporating 30% of CA showed a compressive strength of 24 MPa at 56 days compared to that of 33 MPa for the identical control specimen without CA. This strength decrease was due to the porous nature of the used CA and was compensated for by the incorporation of steel fibers. Specimens with 1% of steel fibers exhibited higher strength properties compared to those with 0.5% of steel fibers for all the tested dosages of CA. The control specimens without CA and steel fibers showed expansions higher than 0.10% and 0.20% at 14 and 28 days, respectively, demonstrating their reactive behavior. The hybrid incorporation of CA and steel fibers decreased the ASR expansion. The mortar bar specimen incorporating 10% of CA and 1% of steel fibers showed an expansion of 0.168% at 28 days compared to that of 0.321% for the control specimen without CA and steel fibers. A decrease in the compressive and flexural strengths was observed for the specimen placed in ASR exposure conditions compared to identical specimens placed in normal water. However, specimens incorporating CA and steel fibers showed relatively fewer effects under the ASR exposure conditions. The control specimens without CA and steel fibers also showed micro-cracking due to ASR exposure, as observed through scanning electron microscopy. This study will assist practitioners to construct a sustainable building using locally available waste materials with the additional advantage of mitigating the ASR-related damages.

Mitigation of alkali silica reactions in concrete using multi-crystalline intermixed waterproofing materials

Concrete deterioration by Alkali Silica Reactions (ASR) is a severe issue of concrete durability associated with porosity and permeability. Most of the industrial solutions for mitigating ASR rely on controlling the mix design by mineral admixtures or lithium compounds. An innovative approach for mitigating ASR through a secondary role of crystalline waterproofing materials is presented. An aqueous solution of Multi-Crystallization Enhancer (MCE) is intermixed with water or added to the concrete mixture, at a dosage of 2% by weight of cement, then upon curing reduces the permeability under pressure by more than 99%. This study shows that ASR mitigation can be accomplished by incorporating the MCE in the fresh concrete mixture or by prewetting the aggregates. The experiments were made according to the methods of ASTM C1260. The investigated independent experimental variables included water to cement ratio, types of aggregates, method of the MCE addition, and time. The MCE can change the performance of aggregates from reactive to be equivalent to non-reactive. The findings demonstrate that the length expansion from ASR increases with increasing the w/c ratio for all types of aggregates attributed to the increase in the permeability. The MCE addition to mixtures with reactive aggregates enhances the resistivity against ASR by a percentage in the range of 45%-77%. The functionality of the MCE in mitigating the ASR is also confirmed using concrete specimens with long term ASR testing (ASTM C1293).

Effect of spent bleaching earth ash on sulphate attack resistance of concrete

One of the severe durability problems of concrete is sulphate attack. Sulphate attack can cause expansion of concrete due to the formation of gypsum and ettringite. Recently, spent bleaching earth ash (SBEA) is being used as a partial cement replacement in concrete. In this study, the effects of unground SBEA (USBEA) and ground SBEA (GSBEA) on sulphate attack resistance on concrete in terms of expansion of mortar bar and loss in compressive strength of concrete exposed to 5% sodium sulphate solution were determined. The SBEA was ground in a planetary grinding ball mill for 30 min to obtain a finer particle size. The expansion of mortar bars exposed to sulphate conditions containing USBEA and GSBEA was evaluated for 6 months according to ASTM C1012. Meanwhile, the compressive strength of concrete containing USBEA and GSBEA against sulphate attack was determined at 28 and 90 days. It was found that the expansion of mortar bars containing GSBEA was the lowest (0.01%) among the specimens. The strength deterioration factor of concrete containing GSBEA against sulphate attack was the lowest, with 1.31% at 90 days. The findings showed that ground SBEA could be used to enhance the sulphate attack resistance of concrete.

The impact of specimen size and alteration of fiber configuration on the flexural performance of high-performance concrete

This study examines the impact of fiber configuration and specimen size on the flexural performance and thus the energy absorption capacity of moderate and high-performance fiber reinforced concrete (FRC). A total of 180 specimens were produced using hooked-end steel fibers in lengths of 30-mm and 60-mm, and 54-mm long macro synthetic fibers. The specimens, in the form of small beams (75 × 75 × 320 mm3), large beams (150 × 150 × 750 mm3), and square panel specimens (600 × 600 × 100 mm3), were tested in accordance with EN14488-5 and ASTM C1609 standards. The results showed that as the amount of fibers increased, the flexural performance of FRC improved significantly, provided that precautions were taken to avoid mixing and placement issues when using higher amounts of fibers. 60-mm hooked-end steel fibers had the best performance among all the fibers tested with higher ultimate and post-cracking flexural strengths. 54-mm synthetic fibers seemed to be a cost-effective alternative with comparable energy absorption performance when compared to 30-mm hooked-end steel fibers. Small beams had a slightly higher ultimate (∼15% more) and post-cracking (∼35% more) flexural strengths than large beams, but the equivalent flexural strength ratio was not significantly affected by the specimen size. No clear relationship between fiber dosage and ultimate flexural strength was observed, but a relationship was observed between the fiber dosage and the equivalent flexural strength ratio, with R2 values ranging from 65% to 93% depending on the concrete matrix and the fiber type. The study also showed strong correlations (R2>91%) between the energy absorption capacity of plate specimens and beam specimens, suggesting that plate specimens can be used to reduce the time and effort required in testing during trial batches and product development. Finally, the use of high-performance concrete does not seem to be necessary, when the target is to improve the energy absorption capacity of FRC, particularly at low fiber volumes.

Influence of Synthetic Fibers on the Flexural Properties of Concrete: Prediction of Toughness as a Function of Volume, Slenderness Ratio and Elastic Modulus of Fibers.

The construction industry requires concrete with adequate post-cracking behavior for applications such as tunnels, bridges, and pavements. For this reason, polypropylene macrofibers are used, which are synthetic fibers that fulfill the function of providing residual strength to concrete. In this study, an experimental plan is carried out to evaluate the bending behavior of concrete reinforced with polypropylene fibers using the four-point bending test according to ASTM C1609. Three fiber dosages (3.6, 7.2 and 10.8 kg/m3) and three fiber lengths (40, 50, and 60 mm) were used. The use of macro polypropylene fibers increased the post-cracking behavior of concrete. In addition, based on the experimentally obtained results and available literature data, a multivariable equation was developed to predict the concrete toughness as a function of the volume, slenderness, and modulus of elasticity of the fibers. A Pearson's correlation coefficient, r of 0.90, showed a strong correlation between the developed equation and the experimental data. From this equation, it was possible to determine the participation of the following parameters in calculating toughness. The participation or weight of the fiber's modulus of elasticity on the concrete's tenacity is 26%, the volume of the fiber is 39%, the slenderness is 19%, and the reinforcement index is 16%.

Flexural Performance of Composite RC Beams Having an ECC Layer at the Tension Face

This paper presents an experimental study on the flexural behavior of composite Reinforced Concrete (RC) beams having a monolithic Engineered Cementitious Composites (ECC) layer at the tension face. Due to the brittle nature of normal concrete, clear cover on the tension side of beam cracks results in spalling and corrosion of reinforcement. The proposed technique overcomes the inherent brittle behavior of normal concrete with the incorporation of ECC on the tension face. This also helps in reducing bond-splitting, cover-spalling, and buckling of reinforcement in RC flexural members. For testing purposes, six full-scale beam specimens (225 mm x 300 mm x 2400 mm) with the same reinforcement were cast and tested. Out of six, two specimens were made of conventional concrete, whereas the remaining four (two each) had an ECC layer of 75mm and 100mm thick at the tension face respectively. Each specimen was installed with three strain gauges (one each at the midspan top & bottom surface of concrete and one midspan rebar on the tension face) and one LVDT at midspan. The samples were then subjected to simple monotonic loading under a third-point bending test as per ASTM C78. The load-displacement, stress-strain and moment-curvature curves were obtained for all the tested specimens. It was found that ECC-strengthened beam samples displayed an increased flexural performance at first crack, yield, and ultimate load-carrying capacity as compared to conventional RC specimens. Whereas a better crack arrest with even distribution of cracks and improvement in ductility was observed for the ECC-strengthened composite beams.

Effect of size and water content on the compressive strength of mortar

Compression tests of mortar specimens were conducted to investigate the effect of size and water content on the compressive strength of mortar in a bed joint. Four types of mortar specimens were tested: cube specimens, cylinder specimens, plate specimens that were cut from cubes, and disc specimens that were cast between masonry blocks. Both Type N and Type S mortar were examined. The water content of the mortar varied from 18 % of the total weight of the mortar mix and the water, up to 24 %, and the nominal thicknesses of the plate and disc specimens varied from 6.35 mm to 22.2 mm. Cube and cylinder specimens were subjected to the standard compression test described in ASTM C109. Plate and disc specimens were subjected to the double punch test described in DIN 18555–9. Test results showed that the mortar compressive strength was strongly dependent on the specimen size and water content.

Mechanical properties and corrosion resistance of recycled aggregate concrete exposed to accelerated and natural marine environment

This paper presents the effect of long-term exposure (simulated and natural) on the mechanical and durability characteristics of ordinary Portland cement concrete (OPCC) with and without recycled concrete aggregate (RCA) prepared using two water-cement (w/c) ratios. Each of the four concrete mixes (i.e. 0.40-R0, 0.40-R30, 0.43-R0 and 0.43-R30) was exposed to the simulated ((i.e. Fog apparatus/chamber as per provisions of ASTM B117) and two natural marine environments (on a water jetty and submerged in the seawater) for a period of 90, 180 and 365 days. To observe the long-term effect of the simulated and natural environment exposure, the exposed specimens were tested for compressive strength, splitting tensile strength, pull-out strength, and half-cell potential test as per the standard testing provisions of ASTM C39, ASTMC496, ASTMC900, and ASTMC876, respectively. The comparison of the results showed that the concrete specimens exposed to the natural marine environment submerged in the seawater resulted in reduced compressive and pull-out strengths, high and increased split tensile strength, and poor resistivity to corrosion as compared to the one placed on a deck of water jetty and simulated marine environment. The concrete prepared by using 30% RCA was significantly affected by the exposures as compared to the natural environment and a difference of nearly 30% in results of compressive strength, split tensile strength, and pull-out strength and a difference of 40% was found in resistivity to corrosion. Similarly, the high w/c ratio also affected the compressive strength, split tensile strength, pull-out strength, and resistivity to corrosion of concrete. The results of microstructure also confirmed that the concrete exposed to a harsh environment underwent severe deterioration, which led to the lessening of the mechanical properties.

Mitigating alkali-silica reaction in cement mortars through microbial carbonate precipitation technique

Alkali-Silica Reaction (ASR) is a major cause of durability reduction in cement mixtures. This reaction takes place between the reactive silica contained in aggregates and the alkaline elements contained in cement (sodium and potassium), producing a hydrophilic gel known as glass water. This gel swells upon absorbing water, causing a damaging internal pressure in the mortar. This study aimed to investigate the impact of Microbial-Induced Calcite Precipitation (MICP) with Sporosarcina pasteurii on the progress of ASR in cement mortars. The mortars were made using the accelerated mortar bar method (ASTM C1260) by substituting 0, 25, 50, 75, and 100 % of aggregates with waste glass, as the extreme material causing ASR. The glass was treated by two methods named Wet Calcite Precipitation (WCP) and Fixed Calcite Precipitation (FCP), which both involved spraying 0.5 ml/cm2 of bacterial suspension on the glass. After 28 days of exposure to alkaline conditions, the mortars were examined by Scanning Electron Microscopy, X-ray Diffraction spectroscopy, and Energy-dispersive X-ray spectroscopy to verify the occurrence of ASR. The mortars were subjected to the expansion test, the ultrasonic pulse velocity (UPV) test, and the compressive strength test to measure their physical and mechanical properties. Both MCP treatments managed to significantly reduce the adverse effects of ASR (compared to the control) at the 95 % confidence level. Between WCP and FCP, WCP was more effective in improving the results of UPV and expansion tests, and FCP was more effective in improving compressive strength. The findings showed that MICP can effectively inhibit the adverse effects of ASR in cement mortars.

Studies on mechanical performance of treated and non-treated coarse recycled concrete aggregate and its performance in concrete-an Indian case study

In India, utilization of construction & demolition (C&D) waste-based coarse recycled concrete aggregate (CRCA) for RCC work is limited up to 20% for M25 grade of concrete as codified in IS 383:2016. However, enhanced utilization is not possible until classification based on quality grading of C&D waste-based aggregate is made available. One of the possible ways to classify C&D waste-based aggregate can be routed based on specific gravity and water absorption value of the parent rock which is generally affected by the adhered mortar. In the present study, C&D waste-based coarse recycled concrete aggregate (CRCA) sourced from two different sources was studied holistically. CRCA aggregates were subjected to mechanical treatment in a Los Angeles machine and Characteristics of CRCA before and after treatment were evaluated and compared. Further, a comparative study in fresh, hardened, and durability stages was conducted on the properties of concrete made with treated and non–treated CRCA. Fresh, hardened, and durability properties of concrete made with C&DW-based CRCA investigated for the (a) Fresh properties – workability in terms of slump, and air content. (b) Hardened properties–compressive and flexural strength, modulus of elasticity, drying shrinkage (c) Durability properties –resistance to chloride (RCPT, as per ASTM C1202), resistance to carbonation as per ISO 1920 Part 12 and resistance to water penetration as per IS 516 Part2 / Section-1. From the study, it can be concluded that physical properties such as specific gravity and water absorption of CRCA can be used as a tool for the grading of C&D waste-based CRCA. Based upon fresh, hardened, and durable behavior of concrete made with CRCA, it was observed that non-treated CRCA can be used up to 40 % for a grade of concrete up to M 30 whereas treated CRCA can be used up to 100 %. This was attributed to the improvement in the ITZ.

Synergistic effect of waste glass powder and fly ash on some properties of mortar and notably suppressing alkali-silica reaction

In this study the mitigation influence of incorporating waste glass powder (G) and class F fly ash (F) in mortar as partial cement replacement on the alkali-silica reaction (ASR) between reactive aggregate and alkali contents of cement were investigated. Waste G and F replaced cement separately and together on mass basis at 10%, 20%, and 30%. The unit weight (28 days), water absorption, porosity, compressive, and flexural strength tests were conducted at 28- and 90-day water curing time on 40×40×160 mm prismatic hardened samples and flow table test on fresh mortar. There was a slight reduction of the unit weight, an increased workability, and decreased water absorption and porosity; a little reduction of the compressive strength and flexural strength were seen after the tests. In addition, the expansions of mortar were measured up to 90 days. When 14 days expansions were considered according to ASTM C1260, addition of waste G and F separately reduced the expansion that occurred due to ASR. However, the mixture containing 15% waste G and 15% F together (GF-30) exhibited the lowest expansion in the order of 0.02% which was far lower than 0.10%. The higher replacement ratio of waste G and F together and separately caused lower expansion in mortar.

Prediction of the cementing potential of activated pond ash reinforced with glass powder for soft soil strengthening, by an artificial neural network model

The effect of Pond Ash (PA) activated with sodium chloride (NaCl) solution and reinforced with glass powder on the mechanical properties of soft clay soil, which comprise of the California bearing ratio (CBR) and the unconfined compressive strength (UCS) has been studied in this research work. The PA requires pozzolanic improvements to meet the ASTM C618 requirements for pozzolanas. In the present research paper, further emphasis has been on the machine learning prediction of CBR and UCS of the soft clay soil stabilized with a composite of PA. Generally, the studied soft clay soil properties, which were the microstructure, microspecter/micrograph, oxide composition, Atterberg limits, compaction behavior, free swell index (FSI), CBR and UCS significantly improved due to the enhanced cementitious ability of the activated and reinforced PA. The multiple data collected from this general stabilization result were used to predict the soil’s CBR and UCS by the artificial neural network (ANN) technique. The results showed high performance of the model in terms of the sum of squares error (SSE) of 1.5% and 2.0% and the coefficient of determination (R2) of 0.9979 and 0.9973 for the CBR and UCS models, respectively. The models also outclassed the performances of other models from the literature.

Flexural behavior of a concrete beam reinforced with metal rebars produced from a pseudo-elastic Nickel-Titanium alloy

The use of concrete in the construction industry is widespread throughout the world, which increases the need for a better characterization of its technical aspects. In particular, there is a need for a better understanding of its poor performance when subjected to dynamic loads, which occurs due to its great stiffness and its little (if any) deformation capacity. Knowing that one of the ways to mitigate the poor behavior of concrete in case of dynamic loads is by improving the deformation capacity or ductility of the metallic reinforcement, the proposal to explore the behavior of a concrete beam reinforced with metallic rebars produced from a pseudo-elastic Nickel-Titanium alloy becomes highly desirable. This experimental research aims to verify the flexural behavior of a concrete beam reinforced with Nickel-Titanium rebars. In this regard, the requirements suggested by the technical standard in force were carefully followed, relying mainly on the international standard ASTM C78. Concrete specimens were produced either reinforced with conventional steel rebars; or reinforced with Nickel-Titanium rebars. The results showed that, although the Nickel-Titanium rebars specimens presented a modulus of rupture 26.48% lower, their displacement was about 642.79% greater in relation to specimens with conventional steel rebars, in addition to presenting a partial recovery of the beam's initial position even after complete concrete breakage.

Analisis Kekuatan Tarik Komposit Laminat Jute Berdasarkan Pola Kerusakan Kolom Silinder Metode Split Tensile Test

The purpose of this study is to obtain the damage pattern of cylindrical column concrete specimens (BKS) reinforced with laminate jute composite (KLJ) based on the results of the Split Tensile Test, to find out the phenomenon of applying laminated jute composite reinforcement to cylindrical column concrete to the percentage of crack patterns ( PPR) specimens, and analyze the comparison between split tensile strength (KTB) and PPR. The test specimens were printed based on the ASTM C496 test standard using the Vacuum Bagging method. Specimen variations consist of 1 to 4 layers of KLJ and one variation without KLJ sheath as a control specimen. The split tensile test used the UTM test tool with each variation being carried out 3 repetitions. PPR observations and calculations were carried out with the help of Adobe Photoshop software. The results of the study show that the greater the KTB value, the greater the PPR that occurs. The increase in PPR in each KTB is reported in this article.

Characterization of Some Portland Limestone Cements in Nigeria Using Fourier-Transform Infrared Spectroscopy (FTIR)

In Nigeria, the most widely used cement strength class are 32.5 and 42.5 Portland limestone cement. However, due to lack of awareness, scientists and researchers are reporting the use of PLC as Ordinary Portland Cement (OPC). Thestudy presents the characterization of PLC using absorption spectroscopy as well as oxide composition. Ratio between 7 -and 28 -day strengths of some selected PLCs are presented. It is seen that the Brands investigated conforms to the specifications of Portland composite cements in compliance with ASTM C150 and NIS 444-1. Absorption spectrum for the two brands were similar to that of OPC and exhibited similar characteristics. Concrete strength was within the designed concrete specification, and the ration between the two curing ages is 0.6 for both brands.

Sulfate Resistance and Alkali-Silica Reaction of Recycled Aggregate Concrete

In this research article laboratory investigations of sulfate resistance and alkali-silica reaction of recycled aggregate concrete are presented. A total of eighteen prisms of 25mm x 25mm x 286mm were prepared using a 1:3 (cement: fine aggregates) mix and 0.4 water to binder ratio. The specimens were prepared in three batches using recycled aggregates, conventional aggregates, and sand. An equal number of samples was used to evaluate sulfate resistance and alkali-silica reaction. The change in length of specimens was measured in a standard way from 1- to 28 days. The results at 14- and 28-days show that the percentile change in length of all specimens is less than the specified limit of concerned standards. The length change recorded at 14 days (in accordance with ASTM C1260 recommendations) of recycled aggregates is 342% (for alkali-silica reaction) and 57% (for sulfate resistance) better than conventional aggregates and sand. Therefore, the performance of recycled aggregates is concluded better compared to conventional aggregates and sand for both alkali-silica reactivity and sulfate resistance.

Experimental study and classification of natural zeolite pozzolan for cement in South Africa

The present study investigated the performance of South African natural zeolite for potential use as a cement extender. To the best knowledge of the authors, the natural zeolite studied has not been employed before as pozzolan in the cement industry, and its proposed use would be new in concrete construction. In the investigation, mortar mixtures were prepared using ordinary Portland cement CEM I 52,5N blended with 0, 10, 20 and 30% natural zeolite. The effectiveness of natural zeolite was also compared with performance results of mixtures containing 30% fly ash. The tests conducted were workability, compressive strength, pozzolanic activity with lime, drying shrinkage, alkali-silica reaction, and sulphate resistance. Analytical studies were done using X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. It was found that, while incorporation of natural zeolite in cement reduces workability, its effects on mechanical properties and on durability characteristics were superior to those of fly ash, as the former effectively enhanced long-term strength and mitigated drying shrinkage, alkali-silica reaction and sulphate attack. Incorporation of 20% natural zeolite in cement gave an effective overall performance, meeting the ASTM C618 (2015) criteria for Class N pozzolan. Based on EN 197-1 (2000) / SANS 50197-1 (2013), the blend of natural zeolite and ordinary Portland cement met the criteria for its classification as CEM II/A-P 32.5N,R cement type.

Deicer Salt-Scaling Resistance of Concrete Using Recycled Concrete Aggregates Pretreated by Silica Fume Slurry.

Concrete wastes such as recycled concrete aggregates (RCA) make up a significant part of construction and demolition waste (C&DW) which can be used to minimize usage of natural aggregates and reduce carbon footprint. This paper studies the salt-scaling resistance of recycled aggregate concrete produced with pretreated RCAs. The test method for evaluating salt-scaling resistance in concrete according to DIN EN 1340: 2003 was performed. Four series of concrete mixes using natural aggregates, RCAs, manually pretreated RCA, and modified RCA in a desiccator were subjected to the different tests in terms of bulk electrical resistance in two directions (X and Y) before and after freeze-thaw cycles, ultrasonic pulse velocity, and weight loss of the surface layer of concrete specimens. Moreover, Scanning Electron Microscopy (SEM) of mixes was conducted and the microstructure of mixes considering the interface transition zone was studied. Results show that after exposure to cycles of freezing and thawing, the quality of concrete regarding ultrasonic pulse velocity did not change. The electrical resistance of specimens decreased significantly in X-direction and slightly in Y-direction after applying freeze-thaw cycles in all mixes. Nevertheless, surface modification of RCAs can increase electrical resistance and improve durability of concrete. SEM images show that the interface transition zone before and after freeze-thaw cycles remained unchanged which means strong bond between aggregate, new mortar, and old mortar. An estimation of the total charge passed indicated that all recycled aggregate concretes can be classified in a safe area and with very low chloride ion penetrability according to ASTM C1202.

Pengaruh Gradasi Pasir Terhadap Kekuatan Tekan Mortar dalam Perencanaan Sementasi Limbah Radioaktif

Utilization of nuclear energy from various fields of life will produce radioactive waste. Radioactive waste management is carried out according to the type and characteristics of the radioactive waste. Immobilization is an example of a method for managing radioactive waste through compacting or solidifying the waste with a specific matrix to bind and contain the radionuclides. The cementation method is a type of technology for the radioactive waste immobilization method that has been used commercially and proven suitable for use. The main component of cementation is the mortar. This paper aims to determine the effect of fine aggregate (sand) gradation on the compressive strength of the resulting mortar. The research methodology was carried out experimentally. Three types of fine aggregate (sand) are used with IPLN 1, IPLN 2, and IPLN 3 codes. Fine aggregate (sand) has been examined for both silt content (material smaller than 0.075 mm in size), organic content, specific gravity, analysis sand gradation, and fine grain modulus (MHB). From the test results, the fine aggregate (sand) gradations for IPLN 1, IPLN 2, and IPLN 3 are slightly coarse sand, little coarse sand, and fine sand. The fine grain modulus (MHB) of the three types of fine aggregate (sand) are 2.58, 2.46, and 1.8. Only fine aggregate (sand) IPLN 3, whose MHB value is outside the ASTM C33 acceptance criteria, ranges from 2.3 to 3.1. The optimum compressive strength values obtained with three types of fine aggregate (sand) variations, IPLN 1, IPLN 2, and IPLN 3, respectively, were 10.292, 9.411, and 6.026 MPa. Keywords: radioactive waste, cementation, sand, gradation, mortar, compressive strength