ASTM C1202 Research Articles

ALKALI-SILICA REACTIVITY OF SOME GRANITIC ROCKS IN KUMASI, GHANA: IMPLICATIONS FOR USE OF ROCK AGGREGATES FOR CONSTRUCTION

This paper seeks to assess the potential of Alkali-Silica Reaction on some granitic rocks in Kumasi in Ghana. Alkali-Silica reactions occur over time between alkaline cement paste and silica contained in rock aggregates as a result of the swelling due to the reaction of certain constituents in the rock aggregates with alkali hydroxides. Alkali-Silica reactions become potentially harmful when they cause significant expansion. Aggregates used for this research were sought from three different quarries, namely, Consar Stone Quarry in Barekese, Nnagot Quarry in Kona and Modern Granite Quarry in Buoho. To achieve the objectives of this project, two test methods were employed such as Accelerated Mortar Bar test (ASTM C1260) and Petrographic analysis. Presence of strained quartz is an indicator for the occurrence of Alkali-Silica Reaction. Samples from Kona contained quite an appreciable amount of strained quartz and exhibited an expansion above the ASTM C 1260 specification, implying that it is potentially reactive and thus not useful for construction works, whilst samples from Barekese, and Buoho were innocuous and may be used for construction works. Supplementary cementing materials such as pozzolans (which are readily available) can be added to concrete mixtures with aggregates from Kona to reduce the harsh effects of ASR.

Carbonation Resistance in Ordinary Portland Cement Concrete with and without Recycled Coarse Aggregate in Natural and Simulated Environment

This research aims to examine the effect of carbonation on the strength properties and carbonation depth of ordinary Portland cement (OPC) concrete using two different water to cement ratios (w/c) and two different replacement percentages of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA). Two concrete mixes were prepared using w/c of 0.4 and 0.43. The two concrete mixes were subdivided into two subgroups based on the use of NCA and 30% RCA. The first concrete mix having w/c of 0.4 was contained NCA and from this concrete, 42 cylinders of 100 mm dia. and 200 mm height were cast. Six out of 42 cylinders served as control specimens and were not exposed to CO2. A total of 18 out of the remaining 36 cylinders was exposed to the simulated environment and the rest were exposed to the natural environment. The second concrete mix having a w/c of 0.4 contained 30% RCA/70% NCA, and using this concrete, 42 cylinders of similar size were cast. A similar scheme was adopted for w/c of 0.43 and, in total, 84 cylinders using four mix designs were cast. After casting and 28 days of curing, six out of 42 cylinders cast from each concrete mix design were tested for compression and splitting tensile strength, following ASTM C39 and ASTM C496 without any exposure to carbon dioxide (CO2). A total of 18 out of the remaining 36 cylinders was exposed to the simulated environment in a carbonation chamber for an equivalent time duration of 90, 180 and 365 days following CEN test guidelines and the other 18 cylinders were kept in the natural environment for a period of 90, 180 and 365 days. After the completion of simulated and natural exposure periods, these cylinders were distributed equally to test for compressive strength and splitting tensile strength to observe the effect of carbon dioxide (CO2) at each time duration (i.e., 90, 180 and 365 days), and replacement percentage of RCA (i.e., 0 and 30%), which showed that carbonation depth increases incrementally with the w/c ratio and CO2 exposure duration. In both the simulated and the natural environment, the use of RCA in concrete cast using a w/c of 0.4 increased carbonation depth up to 38% and 46%, whereas, in the case of the concrete cast using a w/c ratio of 0.43, the use of RCA increased the carbonation depth up to 16% and 25%. In general, the use of RCA in the concrete exposed to the natural environment significantly affected the compressive strength of concrete, due to multiple interfaces and the porous structure of RCA, and the variation in the temperature, humidity and content of carbon dioxide (CO2) present in the actual environment. The maximum compressive strength variation prepared from the mixes M0-0.4, M30-0.43, M0-0.43 and M30-0.43 differed by 5.88%, 7.69%, 16.67% and 20% for an exposure period up to 365 days. Similarly, the results of splitting tensile strength tests on cylinders prepared from the same mixes exposed to the natural environment differ by 7.4%, 27.6%, 25.41% and 18.2% up to 365 days of exposure, respectively, as compared to the simulated environment.

Activation of Blast Furnace Slag with CFB Fly Ash as a Supplementary Binder Material: Hydration Products and Effects of Sulfate Attack

Circulating Fluidized Bed (CFB) combustion is a clean technology for burning, with advantages of adapting to a large variety of fuel, high combustion efficiency, lower NOx emissions, and stable operation. The residue collected from the ash-hoppers of the electrostatic precipitator of the CFB boiler is called CFB fly ash. This paper presents the hydration development on the application of CFB fly ash to activating blast furnace slag (BFS) as a supplementary binder material (SBM) for replacement of Portland cement in making concrete. Investigation of the hydration products of cement pastes prepared with combinations of BFS and CFB fly ash were conducted by means of X-ray diffraction, thermal gravimetric analysis, and scanning electronic microscope. Test results show that the main hydration products of the CFB fly ash-BFS blended pastes were found to be hydrated calcium silicate (C-S-H), ettringite, gypsum, and some portlandite. Considering that CFB fly ash produced from the combustion of high-sulfur coke has high SO3 contents, the volume stability of mortar made from CFB fly ash-activated BFS was subjected to tests in accordance with ASTM C1012 and ASTM C1038 for evaluating the internal and external sulfate attack, respectively. The results indicate that, due to the high sulfur (SO3) content of CFB fly ash, the expansion caused by internal sulfate attack (ISA) increased with increasing proportion of CFB fly ash in the mixture. In contrast, no significant expansion was observed in the external sulfate attack (ESA) test, regardless of the proportion of CFB fly ash in the mixture. In order for the CFB fly ash to serve as a supplementary binder material and to maintain adequate volume stability, the amount of CFB fly ash used for the activation of BFS is recommended to be no more than 20% of the SBM.

Petrological features of volcanic scoriae from the southern part of the Cameroon Volcanic Line and their supplementary cementations application

Volcanic scoriae from the southern part of the Cameroon Volcanic Line (Limbé, Loum-Tombel, Yamba, Doupé, Njinkouo, Foumbot, Manjo-manengollé, Galim and Djoungo) were investigated in order to determine their chemical and mineralogical composition, to deduce their origin and to identify their natural characteristics which may be useful to the cement industry. The mineralogical composition was determined by X-ray Diffractometer (XRD); X-ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) instruments provided geochemical data. In order to establish the relationship between the natural characteristics of volcanic scoriae and the properties of cements, the amount of amorphous phases was determined by dissolution using sodium hydroxide solution and the pozzolanic activity by thermogravimetric analysis. Field observations show that these rocks are basalts, basanites, hawaiites and picrobasalts. Their mineralogical composition includes augite, olivine, plagioclase, enstatite, feldspars, ettringite, portlandite and Fe–Ti minerals. Overall, they are characterized by high MgO, Fe2O3, CaO, and TiO2 contents. The behavior of major and trace elements suggests that volcanic scoriae have an evolution dominated by partial melting. Besides, high chondrite normalized La/Yb (8–22), Tb/Yb (>1.9) and Dy/Yb (>2) values suggest that the melting corresponds to the garnet lherzolite stability field. The scoriae exhibit good pozzolanic reactivity after 28 days according to their considerable amount of amorphous phases, low CaO contents and their large specific surface area. According to ASTM C618 standard, the sum of SiO2, Al2O3 and Fe2O3 (SAI = 65.96–76.34 wt.%); LOI (-0.1–16.99 wt.%), and of CaO, Fe2O3 and MgO (CIM = 23.43–34.06 wt.%) suggest that those less weathered materials seem appropriate as an additive in cement manufacture. The suitable use of volcanic scoriae in the cement industry closely depends on the petrological features of amorphous phases.

Alkaline activation of mortars made from solid construction waste [Activación alcalina de morteros fabricados a partir de residuos sólidos de construcción

In the present investigation the influence of the percentage by weight of replacement of portland cement (PC) by recycled concrete powder (RCP), alkaline activated, in percentages of 10%, 20%, 30%, 40% and 50%, was evaluated. which were selected from construction rubble left in the Buenos Aires spa, Víctor Larco Herrera district, Trujillo province. After being washed, they went to the grinding and sieving process (400 mesh), using only the through material. Specimens were manufactured according to the ASTM C-109 standard for the compression test in cement mortars, for the alkaline solution NaOH (4M) was used. The mortars obtained were cured in an oven at 70 ° C for 72 hours, and subsequently the curing was completed at room temperature, for a total time of 28 days. The results of the average compression test were 12.15 MPa, in the case of the PC mortar and 14.25 MPa in the best case (PC mortar and RCP-10%), the increase being 17.28%. The mix design using coarse sand and binder was kept constant at (3: 1), while the water / cement ratio (w / c) was 0.6 in all cases. The reason for the increase in compressive strength is due to the reaction between the RCP particles, alkaline solution and the calcium hydroxide produced during the hydration of the cement particles, which generate gels (CASH), which occupy the spaces left by the hydration process of the aforementioned cement particles, as they need calcium hydroxide. For all cases of the compression test, a total of 10 repetitions were carried out.

Comminution: A Supplementation for Pozzolanic Adaptation of Sugarcane Bagasse Ash

Sugarcane bagasse ash (SCBA) has commendable potential as pozzolanic material on account of silica as an attractive oxide composition; however, the coarser size of SCBA fractions hinders the fullest potential. In this regard, the choice of the comminution process is inevitable. In the present investigation, three sugarcane bagasse ash samples with a variable loss on ignition (less than 20%), but in compliance with the oxide composition requirement of ASTM C618, were selected to assess the effect of grinding on the particle size of SCBA and, in turn, the pozzolanic reactivity of ground SCBA. Four different methods of pozzolanic reactivity were adopted to evaluate the suitable characteristics of SCBA, enhancing the pozzolanicity. The results of the pozzolanic reactivity of ground SCBA showed that a particle size (D50) lower than 35 μm and particles below 45 μm higher than 60% was a desirable level of grinding in attaining the minimum strength activity index (SAI) (75%). The provided amorphous silica was more than 25%, and oxide composition conformed to ASTM C618. Assessment of the pozzolanic reactivity of SCBA through simple and feasible techniques like the Frattini test and the modified Chapelle test with SAI appears reassuring. The attainment of the suggested level of particle sizes for SCBA through comminution indicates it is a viable method for developing pozzolanic reactivity.

Engineering properties of soil stabilized with cement and fly ash for sustainable road construction

This study presents an experimental study of engineering properties of soil stabilized with cement and fly ash for layers in roadway construction. The fly ash was used in this study satisfies the requirement according to ASTM C618. Five proportion mixes were used in this work with varying quantities of Ordinary Portland cement amounts of 8 %, 10%, and 8% cement combined with fly ash content of 2%, 4%, and 6%. Specified curing periods of 7, 14, 28 days were applied for all types of specimens. Some engineering tests were carried out, such as unconfined compressive strength, splitting tensile strength, stiffness of stabilized soil, SEM, and XRD techniques. SEM images, magnified 3000 times, showed that compacted soil structure was found as small and odd particles arranged without gel bound, while cement-fly ash stabilized soil was covered foam formation due to cement-fly ash crystal, and small particles cannot be observed. The peak intensity of Silicon Oxide was seen in the region 26-28° with an angle of 2. In addition, cement and fly ash significantly improved the mechanical properties of stabilized soils. Finally, the specimen containing 8% cement and 2% fly ash at 14-day curing has a splitting tensile strength greater than 0.45 MPa, satisfying the base layer of road construction requirement according to current Vietnamese standards. The obtained results provided a shred of evidence for capable of using fly ash for road construction in the context of an increase the fly ash in thermal plants.

Effect of the Addition of Agribusiness and Industrial Wastes as a Partial Substitution of Portland Cement for the Carbonation of Mortars.

The present research work shows the effect on the carbonation of Portland cement-based mortars (PC) with the addition of green materials, specifically residues from two groups: agricultural and industrial wastes, and minerals and fibres. These materials have the purpose of helping with the waste disposal, recycling, and improving the durability of concrete structures. The specimens used for the research were elaborated with CPC 30R RS, according to the Mexican standard NMX-C-414, which is equivalent to the international ASTM C150. The aggregates were taken from the rivers Lerma and Huajumbaro, in the State of Michoacan, Mexico, and the water/cement relation was 1:1 in weight. The carbonation analyses were performed with cylinder specimens in an accelerated carbonation test chamber with conditions of 65 +/− 5% of humidity and 25 +/− 2 °C temperature. The results showed that depending on the PC substitutions, the carbonation front advance of the specimens can increase or decrease. It is highlighted that the charcoal ashes, blast-furnace slags, and natural perlite helped to reduce the carbonation advance compared to the control samples, consequently, they contributed to the durability of concrete structures. Conversely, the sugarcane bagasse ash, brick manufacturing ash, bottom ash, coal, expanded perlite, metakaolin, and opuntia ficus-indica dehydrated fibres additions increased the velocity of carbonation front, helping with the sequestration of greenhouse gases, such as CO2, and reducing environmental pollution.

Fiber Reinforced Compressed Earth Blocks: Evaluating Flexural Strength Characteristics Using Short Flexural Beams.

There are ongoing research efforts directed at addressing strength limitations of compressed earth blocks (CEB) that inhibit their deployment for structural applications, particularly in areas where masonry systems are regularly subjected to lateral loads from high winds. In this paper, the authors focus specifically on the extent to which polypropylene (PP) fibers can be used to enhance the flexural performance of CEB. Cementitious matrices used for CEB production exhibit low tensile and flexural strength (brittle) properties. This work investigates plain (unreinforced) and fiber-reinforced specimens (short flexural beams) with fiber mass content of 0.2, 0.4, 0.6, 0.8, and 1.0% and ordinary Portland cement (OPC) content of 8%. The influence of the inclusion of fiber was based on tests conducted using the Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (ASTM C1609). Material properties that were quantified included first-peak strength, peak strength, equivalent flexural strength, residual strength, and flexural toughness. There was an observed improvement in the performance of the soil-fiber matrixes based on these results of these tests. It was also observed that when the fiber content exceeded 0.6% and above, specimens exhibited a deflection- hardening behavior; an indication of improvement in ductility. An equivalent flexural strength predictive model is proposed.

On the design of the fiber reinforced shotcrete applied as primary rock support in the Cuiabá underground mining excavations: A case study

The Cuiabá mine is an underground gold operation located in Sabará (Minas Gerais, Brazil), which began to use fiber reinforced shotcrete as rock support since 2012. In order to carry on a mechanical analysis and to design the steel and polypropylene fiber reinforced shotcrete linings, the work in hand presents an experimental investigation on the mechanical behavior of the applied composite material inside the Cuiabá mine. Through standardized panel tests, the paper evaluates the toughness performance levels for each studied fiber reinforced shotcrete and applies the current design guidelines for mining works. Based on the rock mass classification of the analyzed mine slopes, while the use of 4.2 kg/m3 of polypropylene fiber volume fractions seems to be suitable where fair rock quality is observed, the addition of 25 kg/m3 of steel fibers is more indicated where severe ground movement is expected. On the other hand, a mismatch between the standardized panel tests (ASTM C1550 and EN 14488-5) on the shotcrete design guidelines was also assessed in the present research. The analyzed fiber reinforced shotcrete received different classifications depending on the used standardized panel test, resulting on an overestimation of the PP fiber reinforced shotcrete for the square panel tests. Safety factors can be applied in order to mitigate the possible mismatch between square and round panel tests.

In situ flexural failure of unbonded fibre reinforced shotcrete linings in response to point loading

In shotcrete lining design there are a number of analysis methods available to estimate the ultimate point load resistance. However, little experimental evidence is available to confirm the validity of these estimates. To address this deficit, a series of full-scale load tests were undertaken on macro-synthetic fibre reinforced shotcrete (MSFRS) linings constructed in an underground coal mine in Queensland, and steel fibre reinforced shotcrete (SFRS) linings constructed as part of a tunnel project under construction in Sydney, Australia. Areas of lining were tested to destruction to identify the point load resistance. All the tests reported in this paper involved predominantly flexural failure of the shotcrete lining.The tests comprised regions of ∼70–100 mm thick FRS lining with bolts placed orthogonally at ∼1000–2500 mm centres. Load was applied using an inflatable lifting bag with a load capacity of about 500kN and maximum displacement capacity of 150 mm. Although the FRS used in the trials displayed post-crack strain-softening behaviour in accompanying ASTM C1550 tests, all the in situ tests resulted in strain-hardening behaviour with no evidence of a dip in load resistance upon cracking of the concrete matrix. The peak load resistance was many times greater than the load resistance measured at first crack, which was confirmed with numerical and analytical modelling. Substantial post-peak ductility was noted in all the tests.

Modelling chloride penetration resistance of Supplementary Cementitious Concrete and compressive strength with pulse velocity

Permeability is one of the principal factors related to durability of concrete. The responsible factor for volume change is permeability. This paper attempt to mechanical and durability study of Supplementary Cementitious Concrete where cement has been replaced by fly ash & GGBS in combination of (30%, 0%), (20%,10%), (10%, 20%) and (0%, 30%).16 such concrete samples has been cast in which water binder ratio introduced as 0.35, 0.40, 0.45 & 50 for each 4 set .cubical and cylindrical concrete 16 samples has been prepared for curing period of 7 and 28 days with replacement of manufactured sand and coarse aggregates. Compressive strength, ultra sonic pulse velocity test (UPV) and Rapid chloride permeability test has been done value at the end of each curing period. The results of this research show that both UPV and compression strength have augmented with supplementary Cementitious materials (SCM) Incorporations. Various empirical models were proposed for pulse velocity and compressive strength. Models for the compressive strength and ultrasonic pulse velocity was developed at individual percentage levels (fly ash or GGBS) and then for each replacement stage four different models (FA percent + GGBS percent) were developed. Similarly after curing for 28 days, Chloride permeability test as per ASTM C1202 has been done. Diverse parameters mathematical models were developed to acknowledge the effect of various factors like SCM incorporations, water binder ratio, replacement of manufactured sand etc., and Models has been tested in full range by data and has strong precision, correlation with experimental data.

A geochemical assessment method for identification of natural pozzolans as supplementary cementitious material

Pozzolans are available in natural resources as raw materials that are potentially applicable in the cement and concrete industries. Proper identification and exploration methods are crucial in relation to their technical and economical purposes. In this paper, a two-phase study is employed, based on geochemical data processing and experimental investigations. Chemical and petrography of natural pozzolans were utilised to develop the proposed method. This method proposes three geochemical indexes: the limiting values of silica/calcium oxide (SiO2/CaO), alumina saturation and alkali content to qualify the natural pozzolan according to the supplementary cementitious requirements. Then, based on ASTM C618 and EN 196-5 standards and complementary tests, the chemical and physical properties of two natural pozzolans were assessed to validate the proposed method. The results showed that this method could be used as a robust and direct way to identify natural pozzolans.

Investigation on the flexural toughness evaluation method and surface cracks fractal characteristics of polypropylene fiber reinforced cement-based composites

In this study, the compressive and flexural properties of polypropylene fiber reinforced cement-based composites are investigated, and a suitable method for evaluating the flexural toughness is proposed. The compressive strength, flexural strength, deflection, flexural toughness, and equivalent flexural toughness ratio are also measured. The results indicate that the addition of 2 % polypropylene fiber and 60 % fly ash into matrix facilitates an improvement in strength, and such a cement matrix shows better crack resistance and flexural toughness than ordinary concrete. JSCE-SF4 and ASTM C1609 methods are the main methods for calculating the flexural toughness, but their single calculation process limits the application range. Therefore, based on JG/T 472–2015, a simple method which is not limited by deformation and can ignore the influence of load fluctuation, is proposed to evaluate the load carrying capacity and flexural toughness of engineered cementitious composites (ECC) in the strain-hardening stage. Furthermore, it is verified that the surface cracks of specimens under flexural load exhibit fractal characteristics, and the “fractal dimension” can be used to describe the distribution of surface cracks. Besides, a quantitative relationship is established between the fractal dimension of surface cracks and the flexural toughness evaluation parameters obtained by the improved JG/T 472–2015 method, which indicates that the fractal dimension of surface cracks can be used to characterize the flexural properties of ECC.

Critical Evaluation for Grading and Fineness Modulus of Concrete Sands used in Sulaymaniyah City-Iraq

Fine aggregates used for concrete works in Sulaymaniyah city frequently fail to meet the standard requirements for gradation and fineness modulus in cement concrete. This paper aims to critically evaluate gradation, fineness modulus, and clay contents of various natural sands produced and used for concrete work in the region. Sixteen field sand samples were collected from various sites in Darbandikhan (5 samples), Qalat Dizah (5 samples), Koysinjaq (5 samples), and Piramagroon (1 sample) confirming to ASTM D75. The field samples were parted into test specimens based on ASTM C702. Then, sieve analysis was carried out on the oven-dry test specimens in compliance with ASTM C136. The test results of fine aggregates were compared with American, British, and Iraqi specification standards using ASTM C33, BS 882, and IQS No. 45. It was revealed that only three sands satisfy the ASTM gradation limits while others do not comply and are on the coarser side. Also, eight samples meet the requirements recommended by BS 882, whereas five samples meet limits by IQS No. 45. It was found that only three sands have the fineness modulus within the ranges recommended by ACI 211.1 and ACI 211.4, while the others have high values. Furthermore, it was found that all sands include an allowable amount of finer particles passing sieve size 0.075 mm. In order to improve particle size distributions, it is recommended to use the blending method to obtain a suitable fine aggregate from two or more failed sands.

Lightweight masonry block without Portland cement

ABSTRACT Huge amounts of fly ash - a substance that does not conform to the ASTM C618 classification due to its chemical properties - have been abandoned in landfills around the world, despite their self-cementing property. It has not been used in concrete making applications due to its large amounts of free lime and sulfate contents. The fly ash in these plants is dumped in landfills, causing serious environmental hazards. Fly ash is disposed to the landfills by belt conveyors after being humidified with water. Therefore, the fly ashes humidified in the landfill areas are hydrated in nature. This hydration is further intensified in landfills by rain and snow. Thus, the free lime content of fly ash decreases due to its long hydration process. In this work, the lightweight masonry blocks were produced by mixing normal and hydrated fly ashes or normal, hydrated fly ash and lime without Portland cement. The compressive strength, water absorption, sorptivity, density, porosity, and thermal conductivity values of the samples produced were determined. The results obtained from these tests showed that lightweight masonry blocks could be produced by using these waste materials in building applications.

Long-term effect of accelerator content on flexural toughness of steel fiber reinforced shotcrete for tunnel construction

Shotcrete is widely used in underground and tunneling applications due to their superior flexural properties and impact resistance. There is a higher need in improving these properties by adding various admixtures and fiber reinforcements to achieve superior performance to accomplish faster turnout in tunneling constructions. In this study, the effect of three accelerators on the long-term flexural performance of steel-fiber reinforced shotcrete were investigated. The types of accelerators used were aluminate, cement mineral, and alkali-free accelerators, whose effects on the flextural properties were investigated over the periods of 1, 3, 6, 12, and 24 months. The flexural toughness was first estimated in accordance with JSCE SF-04, where up to span/150 deflection area under the load-deflection curve was used for calculating the flexural toughness. Whereas ASTM C1018–97 was used to evaluate the first-crack and post-peak load toughness behavior with three specified points for better understanding the flexural behavior of all mixtures. Moreover, it is important to use alkali-free accelerators in terms of both the long-term performance of the tunnels and the safety of the workers. The long-term performances of the specimens showed by the compressive strength and flexural strength were comparable. Finally, according to the long-term effectiveness and performance, the best mix design for the tunnel construction sites is also proposed.

Frost resistance of layered concrete systems incorporating ECC as overlay materials

Concrete structures are subjected to severe durability issues and freeze-thaw action is one of these detrimental issues. In this paper, the behavior of high-volume Class-F fly ash (FA) and slag (SL) incorporated Engineered Cementitious Composites (ECC) as overlay materials was assessed when they were under cyclic freezing and thawing effect. Silica fume concrete (SFC) was also tested as a control mixture which is generally used for overlaying purposes. Layered ECC/substrate concrete (SC) and SFC/SC beam specimens were produced and subjected to 300 freeze-thaw cycles in accordance with ASTM C666, Procedure A. Laboratory tests performed using the layered specimens were based on the determination changes of (i) residual mechanical properties (flexural strength -mid-span beam deflection curves), (ii) ultrasonic pulse velocity (UPV), (iii) mass loss, (iv) relative dynamic modulus of elasticity (RDME) and (v) durability factor (DF). Test results show that all layered specimens produced with different ECC mixtures safely survived 300 freeze-thaw cycles without any disturbance between the ECC overlay and SC interface. On the other hand, one out of six tested SFC/SC layered specimens survived 300 freeze-thaw cycles and final failure for five failed specimens took place from the interfacial planes. Significantly better frost resistance of overlaid systems produced with ECCs than those with SFC was also verified with all of the tests proposed. Between different ECC mixtures, those produced with slag performed better than that those with Class-F fly ash.

Complex Maturity Method for Estimating the Concrete Strength Based on Curing Temperature, Ambient Temperature and Relative Humidity

The maturity method is deservedly considered one of the reliable indirect methods for determining the strength at the early stages of concrete curing. The main parameter in the calculation is the internal temperature of concrete that accumulates during the chemical reaction of concrete curing, while external factors such as ambient temperature and relative humidity are fallaciously omitted. In this work, the complex maturity method was developed based on ASTM C1074, accounting for the influence of ambient temperature and relative humidity and coefficients indicating their influence weight. The laboratory testing to measure the concrete strength by compression method and non-destructive sclerometer method were performed on concrete samples according to ASTM C109, GOST 22690, and GOST 10180. According to the calibration dependence of the existing and proposed methods results in comparison with the strength of cubic samples, the highest coefficient of determination R2 = 0.976 was revealed for the complex method of maturity, which indicates its reliability in contrast with sclerometer and traditional maturity methods. The determination of complex maturity allows for an evaluation of the current state of concrete strength, but also reduces the waiting time for concrete curing and increases the economic effect during construction.

Influence of Tefla Content as Partial Replacement of Fine Aggregate on Performance of Concrete

Concrete is the most widely used material, Natural aggregate consists of up to 80% of the volume of concrete. Given the increasing depletion of natural aggregate, Fine aggregate is a prime material used for preparation of concrete and which plays a major role in mix design. Tefla is considered alternative material satisfy properties of fine aggregate and available easily, domestically with a great amount in OmAlrozam, a town near the city of Derna, Libya. The tefla were ground to roughly fine aggregate fineness, sieve analysis in ASTM C33 requirement of fine aggregate and tefla. physical tests were conducted and chemical composition of the tefla material was determined using X-Ray Fluorescence (XRF). This study aimed to investigate the suitability of tefla, I think is missing partial fine aggregate replacement on performance of concrete, the yellow tefla utilized in its dry condition (without pre-wetting). Four replacement levels, 2.5%, 5%, 7.5%, and 10%, were compared with the control specimen of w/c ratio 0.50. The mechanical and physical properties tests were performed after 7 and 28 days of curing in water. Results showed that concrete containing tefla as partial replacement of fine aggregate compare favourably well with the control specimen. Consequently, it is suggested that tefla can be used as replacement of fine aggregate in the production of concrete.