Days Of Moist Curing Research Articles

Effect of waste glass powder as partial replacement of cement & sand in concrete

The use of waste materials in concrete is now a global trend for effective waste management in order to create a sustainable, eco-friendly concrete. This has the added benefits of protecting natural resources by means of producing more sustainable concrete that has better mechanical properties. This study investigates the characteristics of concrete that contains waste glass powder (WGP) as partial replacement of cement and sand. Laboratory tests were performed to determine the compressive strength and split tensile strength of concrete with 0%, 5%, 10%, 15% and 20% partial replacement of cement and sand separately by WGP after 7, 28, 60 and 90 days of moist curing. Microstructural investigations of X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were performed to determine the effect of WGP on the microstructure of concrete. Results has shown that compressive strength of concrete can be improved to a considerable value at 7, 28, 60 and 90 days when WGP is used as partial replacement of cement by 5%, 10% and 15%, which can be considered as a reasonable amount in producing sustainable concrete. Further replacement percentages resulted in a decrease in compressive strength. WGP enhances the microstructure of concrete in the term of pozzolanic activity and decreasing the microcracks.

Seawater-Mixed Lightweight Aggregate Concretes with Dune Sand, Waste Glass and Nanosilica: Experimental and Life Cycle Analysis

The use of alternative and locally available materials is encouraged in the construction industry to improve its sustainability. Desert regions with shortages in freshwater and river sand as fine aggregates in concrete have to search for alternative materials such as seawater, dune sand, and waste glass powder to produce lightweight concretes. The potential negative effects of adding these alternative materials can be reduced by adding nanosilica to the cementitious system at very low quantities. This study evaluates the feasibility of using these alternative materials and nanosilica (NS) in producing lightweight aggregate concretes (LWACs). A systematic study was carried out to understand the synergistic effect of nanosilica and seawater in improving the hydration characteristics of the developed cementitious systems. Also, the effect of these alternative materials on the fresh properties of the cementitious system was assessed by slump flow tests. The evolution of compressive strength at early ages was investigated after 2, 7, and 28 days of moist curing and an improvement in the strength development in concretes with seawater was observed. Furthermore, the integrity of the developed LWACs was analyzed using oven-dry density, thermal conductivity, water porosity and shrinkage measurements. Moreover, the capillary porosity and sorptivity measurements revealed the denser microstructure in the nano-modified seawater lightweight concretes. In the end, the life-cycle assessment study calculated the benefit of alternative materials in terms of carbon footprint and water consumption. As an outcome, a sustainable solution for producing LWACs containing seawater, dune sand or glass powder was proposed.

Effect of the structuration rate on dimensional stability and mechanical performance of 3D printed mortars

Digital concrete fabrication is a novel construction technique in which structural elements are built layer by layer without the use of formwork. This technology has introduced new challenges in materials engineering. More emphasis lies on the structuration behavior of cement-based materials. Concrete is designed to achieve adapted workability to flow during the pumping phase. It also requires proper build-up and stiffness to retain its shape after extrusion and sustain its own weight and, subsequently, the weight of successive layers. A high degree of structuration is recommended to ensure high printing quality. However, this may adversely affect the performance of the multi-layer printing process. In the present study, an experimental program was carried out to evaluate the impact of structuration rate on the dimensional stability and mechanical properties of the printed element at both early age and long term, respectively. Four different mixtures with various structuration rates were designed and printed. In the fresh state, variations in the layer’s height and width were recorded to evaluate the dimensional stability of the printed structure. On the other hand, several specimens were cut out of the freshly printed elements for mechanical tests. The compression and flexural tests were conducted after 7 and 28 days of moist-curing. The obtained results showed that there exists an optimum rate of structuration above which the quality of the bonding interface is compromised, generating losses in mechanical properties. Under this threshold, anisotropic behavior dominates, leading to low dimensional stability.

Experimental studies on confined compressive strength of Stainless Steel Wire Mesh (SSWM) wrapped concrete columns

The findings of an experimental evaluation of the axial compressive strength of an M25 grade Plain Cement Concrete (PCC) column confined with locally available Stainless Steel Wire Mesh (SSWM) are presented in this paper. Various types of Fiber Reinforced Polymer (FRP) are usually employed to strengthen the load-bearing components of concrete structures. However, these FRP materials exhibits brittle failure and debonding of FRP strip or wrap. Stainless Steel Wire Mesh (SSWM), on the other hand, is a cost-effective substitute for FRP materials when it comes to strengthening of structural elements. In this study, effectiveness of SSWM for confinement of concrete columns is demonstrated through experimental study. For the research, column specimens with a diameter of 150 mm and a height of 300 mm are used. Test specimens are strengthened with one-layer circumferential wrap of SSWM. Three variants of SSWM i.e. SSWM 30 × 32, SSWM 40 × 32 and SSWM 50 × 34 are considered for the study. After 28 days of moist curing, SSWM is applied to the column surface using epoxy SIKADUR 30LP. Axial compressive load-carrying capacities of strengthened specimen are compared with that of control specimens. From the comparative study it is found that SSWM 40 × 32 performs better compared to other variants of SSWM considered for this study. Compared to the control specimen, the load-carrying capacity of the column strengthened with SSWM 40 × 32 is increased by 29.35%. For all the specimen, failure patterns are observed in addition to the load–displacement and stress–strain behaviour. Results of present experimental investigation establishes the suitability of SSWM for confinement or strengthening of concrete elements subjected to compression.

The Influence of Nanoclay and Powdered Ceramic on the Mechanical Properties of Mortar

The amount of concrete utilized worldwide has lately grown due to rising populations and urbanization. The gas emissions during cement manufacturing and the usage of common resources result in a significant environmental threat. As a result, researchers are attempting to minimize the amount of cement consumed by using waste materials while lowering building costs. This research aims to minimize the amount of cement used in concrete by partially replacing it with ceramic powder waste while also increasing the mechanical qualities of concrete mortar by substituting cement with nanoclay hydrophilic bentonite. Mortar samples were prepared using five different replacement percentages of cement by nanoclay, including 0, 2, 4, 6, and 8%, and two replacement percentages of cement by ceramic powder, including 0% and 20%. Compressive and flexural strength tests were performed on mortar samples for 7, 14, and 28 days of moist curing. The toughness was also measured for all mixes by measuring the area under the load-deflection curve. Also, water absorption and relative densities for all mortar mixes were measured. The results show that replacing cement with 2% nanoclay and 20% ceramic powder increases the flexural strength by 11%. Doi: 10.28991/CEJ-2022-08-07-08 Full Text: PDF

Comparative Study of Mechanical Properties of Concrete Using Marble Dust as Partial Cement Replacement and Addition of Polypropylene Fiber

Ordinary Portland cement (OPC) is used as the primary binder to produce concrete. The amount of the CO₂ released during the manufacture of OPC is in the order of one ton for every ton of OPC produced. Attempts made to reduce the use of OPC in concrete are receiving much attention due to environment related issues. In the present study marble dust is used as a partial replacement for cement. It has been estimated that several million tons of Marble Dust are produced worldwide from extracting to finishing process. Hence its utilization has become an important alternative material because of its cement like properties. Marble dust is also easily available at very less cost. Concrete is characterized by quasi-brittle failure i.e; once failure is initiated; nearly complete loss of loading capacity takes place. By addition of randomly distributed fibers in the concrete matrix concrete can be modified to perform in a more ductile manner which prevent and control initiation, propagation and coalescence of cracks. The fibers prevent surface cracking through bridging action leading to an increased resistance of the concrete. This paper presents results of an experimental program to determine mechanical properties of concrete as cement is replaced with marble dust with known percentages (0%, 5%, 10%, 15%) [5] [6] for the grade of M30 and addition of polypropylene fibers of different percentage (0%, 0.5%, 1%, and 1.5%). The concrete test samples were submitted to compressive strength tests after 7 and 28 days of moist curing, as well as flexure and splitting tensile strength tests. Overall Strength of Concrete (Compressive, Tensile & Flexure) showed a reasonable increase upto a limit of 10% for Marble Dust and 0.5% for PP Fibers [1].

Effect of elevated temperature on the calcined clay-limestone and marble stone blended cement concrete

ABSTRACT The impact of high temperatures on calcined clay-limestone cement concrete (LC3) and calcined clay-marble stone cement concrete (MC3) is studied in this paper. In the present study, M25 and M35 grades of concrete was prepared using LC3 and MC3 cement and ordinary Portland cement (OPC). After 28 days of moist curing, prepared cubes of size 100 × 100 × 100 mm3, which were subjected to 100°C, 200°C, 400°C, 600°C and 800°C temperatures. Scanning electron microscopy (SEM), mass loss, surface texture and compressive strength (CS) were studied before and after specified temperatures. The X-ray diffraction (XRD) patterns, thermogravimetric analysis (TGA) and Fourier transformed infrared (FTIR) spectroscopy have been studied over M25-OPC, M25-LC3 and M25-MC3 concrete. The result shows that when the temperature exceeds 400°C, the mass loss in OPC was more than LC3 and MC3 concrete. CS was more in LC3 and MC3 concrete than OPC concrete at all high temperatures. The SEM results reveal that M25-LC3 and M25-MC3 concrete specimens have a sound structured C–S–H gel at high temperatures as compared to M25-OPC concrete specimens.

Use of Natural Minerals to Immobilize Bacterial Cells for Remediating Cracks in Cement-Based Materials

Cracks in cement-based materials are one of the main factors affecting the durability of structure. Recent research in the field of concrete materials showed that self-healing in cement-based systems can be achieved by triggering biogenic calcium carbonate (CaCO3) precipitation. The goal of this study is to establish a comparative evaluation of the use of sepiolite, bentonite, and diatomaceous earth (DE) as an immobilization barrier of Sporosarcina pasteurii (S. pasteurii) cells to trigger self-healing in cement-based systems. For the first time in the literature, this study will provide insight into the use of natural minerals, such as bentonite and sepiolite, as protective carriers for vegetative S. pasteurii cells in cement-based materials and present a comparative evaluation of factors influencing crack healing, such as the microstructure and composition of immobilization barriers. A two-phase self-healing bioadditive was obtained by immobilizing vegetative S. pasteurii cell samples on natural porous minerals with or without the use of required nutrients. Then the samples were cracked by a three-point bending test, and the healing process was screened via stereomicroscope imaging and ultrasonic pulse velocity (UPV) testing after subjecting the cracked samples to 28 days of moist curing. Flexural cracks induced in mortar samples were filled with biogenic precipitate. Relatedly, the water absorption capacity of the samples was decreased in mortar samples containing bacterial cells, the nutrients were added in the curing solution. Fourier transform infrared spectroscopy and scanning electron microscopy analyses showed that calcite was the predominant polymorph of CaCO3 sealant in cracks.

Evaluating composite nanomaterials to control corrosion of reinforcing steel using different tests

There is limited research on the utilization of composite nanomaterials to control corrosion of reinforcing steel in concrete. Therefore, this work was initiated to evaluate the composite nanomaterials (zinc oxide and titanium dioxide) to control corrosion deterioration in reinforced concrete using different tests. The composite nanomaterials were utilized as coating cover over the reinforcing steel surface using two methods of nanofilms and nanoparticles. Fourteen reinforced concrete prisms (100 ×100×300 mm) with central reinforcing steel coated with nanocomposite were casted using w/c ratio of 0.45. After 28 days of moist curing, the prisms were exposed to an accelerated corrosion process using an electrical current supply. The ability of nanocomposite to control corrosion was evaluated using different tests including crack width, ultrasonic pulse velocity (UPV), half-cell potential (HCP) and pullout test. The experimental results showed that nanocomposite materials coated over the reinforcing steel surface significantly reduced the corrosion level of the reinforcing steel in concrete. The non-destructive tests (UPV and HCP) showed significant difference between the nanocoated and uncoated specimens. The damage index of the UPV of the corroded uncoated prisms showed higher values than those of the corroded coated prisms. The HCP values of the nanocoated prisms after corrosion showed significantly lower negative values than those of the control uncoated prisms. Moreover, prisms coated with nanocomposite revealed less corrosion crack width and attained higher ultimate bond load compared to the uncoated prisms. The composite nanolayer coated on the reinforcing steel surface showed higher performance to control corrosion compared to the single nanolayer coated on the reinforcing steel surface. Scanning electron microscopy images showed more homogeneous filling layers of the composite nanolayer coating compared to the single nanolayer coating.

Engineering and Durability Properties of Modified Coconut Shell Concrete

Making low-cost concrete from coconut shell ash and coconut shell aggregate increases sustainability and reduces pollution. This research investigates untreated Coconut Shell Particles (CSP) incorporated with coconut shell ash (CSA) to improve the durability properties at elevated temperatures and in sulphuric acid. Initially, the physical and mechanical properties of cube and cylinder specimens after 7, 28, 56, and 90 days of moist curing were studied. The durability properties were then carried out after the pozzolanic component of CSA in modified concrete was activated. CSA and CSP were used as partial substitutes for ordinary Portland cement and coarse aggregate in class 30 concrete with a constant water to cement ratio of 0.55. Concrete mixes included control, 5% CSP, 10% CSA, and a mixture of 5% CSP incorporated with 10% CSA. According to test results, adding 10% of CSA to CSP concrete decreased the workability, density, and water absorption properties compared to the rest of the concrete mixes. However, these results were within acceptable limits. The compressive strength of 10% CSA concrete at 90 days of moist curing was reduced by 3.23% when 5% CSP was added compared to control. The addition of 10% of CSA to 5% CSP concrete improved the split tensile strength by 2.76% higher than concrete with only 5% CSP. Concrete containing the combination of 10% CSA and 5% CSP showed a 9.37% increment in the split tensile strength compared to concrete having only 5% CSP after sulphuric acid exposure. Also, the compressive strength of 10% CSA and 5% CSP concrete improved by 30.7% when the temperature was elevated to 500 °C for 1 hour compared to the control concrete. Moreover, the reduction in the compressive strength after exposure to the elevated temperature of 500 °C for 1 hr. was still much less by an average of 75.38% compared to other waste materials blended into the concrete by previous works. Doi: 10.28991/CEJ-2022-08-02-013 Full Text: PDF

The effect of polypropylene fibres and coconut coir on restrained shrinkage and compressive strength of concrete

This paper investigates the comparative effects of the use of polypropylene fibres and coconut coir on restrained shrinkage and compressive strengths of concrete. Polypropylene fibres and coconut coir were cut (20 and 40 mm lengths) using 0.05 and 0.1% volume fraction of cement and were added to the concrete mix to cast 27 concrete prisms each for the two restrained shrinkage tests (100 mm × 100 mm × 300 mm). 108 Samples of concrete cubes (100 × 100 × 100 mm) containing 0, 0.05 and 0.1% volume fractions of polypropylene and coconut coir (20 mm and 40 mm in length) were also cast for compressive strength test. Concrete substrates and 8 mm mesh reinforcements were separately used to provide restraints for the concretes prepared for shrinkage tests. The shrinkage tests were monitored for 18 h and compressive test were carried out after 7, 14, 21 and 28 days of moist curing of concrete cubes. The results showed that prisms with substrates containing 0.1% polypropylene fibres and coconut coir reduced shrinkage by 31% and 15%, respectively. For wire mesh-reinforced prisms, 0.1% polypropylene and coconut coir decreased shrinkage by 16% and 7%, respectively. The compressive strength results also showed that polypropylene exhibited better strength performance than coconut coir.

Compressive Strength, Splitting Tensile Strength, and Chloride Penetration Resistance of Concrete with Supplementary Cementitious Materials

This article presents the outcomes of a study that examined the durability and mechanical characteristics of self-consolidating concrete (SCC) mix in which a percentage of the required ordinary Portland cement (OPC) was substituted with either fly ash or ground granulated blast furnace slag (GGBS). The first part of the study evaluates the chloride penetration resistance and compressive strength of SCC mixes in which OPC in a designed control mix was partially replaced in a series of mixes by fly ash in percentages ranging from 10% to 40%. It noted that replacing OPC with fly ash at each of the four percentages studies improved chloride resistance of concrete compared to the control mix made of 100% OPC as binder. The 40% fly ash mix was the best performer in terms of resistance to chloride migration in contrast with the 100% OPC mix. Samples prepared using the 40% fly ash mix SCC mixes had the lowest compressive strength after 7 days of moist curing. However, the 28-day compressive strength of 40% fly ash mix was a healthy 55.75 MPa, only slightly lower than the 100% OPC mix. Tests also showed that adding 2% or fewer basalt fibres to the SCC mix in which 40% of OPC improves concrete resistance to chloride migration in contrast with the 40% fly ash mix that didn’t contain basalt fibres. This paper also reports the relationship between splitting tensile strength and compressive strength of SCC mixes in which up to 80% of OPC was substituted with GGBS. A total of eight mixes were produced by varying the amounts of GGBS used to replace the OPC content of the control mix. The fresh properties were assessed through the flow test, visual stability index (VSI), and the T50. An empirical relationship was developed to predict the splitting tensile strength based on 28-day compressive strength, and its accuracy was evaluated in comparison to formulas in various design codes.

The utilization of walnut shells as a partial replacement of sand in mortar mixes

AbstractThe effect of walnut shells on different properties of mortar was investigated through several experimental tests. The investigated properties include dry density, thermal conductivity, compressive and flexural strengths. Percentage replacements of the walnut shells to sand ratio were 5, 10, and 15%. The walnut shells used in this study were treated by soaking in boiling water for two periods: 1/2 hr and 1 hr. All mortar mixes have same proportion of 1:3:0.7 by weight for cement, sand, and water, respectively. The test results showed that the use of 15% walnut shells treated for 1/2 hr lead to decrease of the density and thermal conductivity of mortar by 15 and 31%, respectively. On the contrary, the compressive and flexural strengths of mortar were decreased by 17 and 25%, respectively, in comparison to the control mortar after 28 days of moist curing. This study leads to a conclusion that by soaking the walnut shells in boiling water for 1/2 hr enhanced the behavior of mortar compared to the un‐soaked ones. This results in achieving an acceptable strength, good thermal insulator, and environmentally friendly mortar.

Influence of Sulfate Ions on Chloride Attack in Concrete Mortars Containing Silica Fume and Jajrood Trass

The effect of sulfate ions on chloride penetration has not been investigated in detail. In this research, standard ordinary portland cement (OPC) mortar and partial cement replacement by silica fume (7.5%) and trass a natural pozzolan (17.5%) were used to investigate the effect of sulfate ions on chloride attack. After 28 days of moist curing, specimens were subjected to chloride–sulfate solutions for 60, 120 and 180 days. According to the results after 208 days, the sulfate intermediate leads to decreased chloride attack in the control and a slight increase in silica fume samples. Regarding the trass sample, an intermediate state occurred. Silica fume reduces chloride penetration significantly. Trass samples generally show better performance than the control in this respect. Rapid chloride migration test (RCMT) was used to determine a method to evaluate the samples behavior in combined chloride–sulfate solutions, quickly. According to the results, RCMT was not an appropriate test to determine chloride penetration in combined chloride–sulfate solutions.

Evaluating corrosion deterioration in self-compacted reinforced concrete beams and prisms using different tests

There is a limited reported research on the corrosion deterioration of self-compacted concrete (SCC) compared to conventional vibrated concrete (CVC). Therefore, this work represents a novel and innovative research to evaluate the corrosion deterioration of reinforcing steel in SCC compared to CVC using different tests. Sixteen reinforced concrete (RC) beams (100 × 150 × 1000 mm) and 16 RC prisms (100 × 100 × 400 mm) were casted using two w/c ratios (0.35 and 0.45) and two concrete types (SCC and CVC). After 28 days of moist curing, the beams and prisms were exposed to accelerated corrosion process using direct current supply. Different tests were performed to detect the corrosion deterioration in the RC specimens including crack pattern and width, ultrasonic pulse velocity (UPV), half-cell potential (HCP), and structural performance (flexural test for beams and pullout test for prisms).The innovative study showed that the SCC specimens (beams and prisms) exhibited higher performance in controlling the corrosion in comparison with CVC beams and prisms. The non-destructive tests (UPV and HCP) showed significant difference between the corroded SCC and CVC specimens. The damage index of the UPV of the corroded CVC beams showed higher values than that of the corroded SCC beams. The HCP values of the corroded CVC beams showed lower negativity than those of the corroded SCC beams. Flexural tests of corroded SCC beams showed higher performance than those of corroded CVC beams. Pullout behavior of corroded SCC prisms showed higher performance compared to corroded CVC prisms. As expected, the CVC and SCC specimens at w/c of 0.35 showed improved corrosion performance compared to the CVC and SCC specimens at w/c of 0.45.

Accelerated Carbonation Assessment of High-Volume Fly Ash Concrete

The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation depth appeared to decrease with increase in compressive strength, but this correlation was not significant.

The effects of calcium stearate on mechanical and durability aspects of self-consolidating concretes incorporating silica fume/natural zeolite

Moisture and aggressive ions transfer into concrete can be considered a significant threat to the durability of self-consolidating concretes (SCCs). To restrict moisture and aggressive ions transfer into concrete, utilizing damp-proofing agents is expected to be beneficial. These admixtures can decrease permeability of concrete, especially the permeability under non-hydrostatic condition, by providing a water-repellent layer along the capillary pores. This study investigated the impacts of calcium stearate (CS), as a damp-proofing agent, on durability properties of SCCs which were prepared with various types of supplementary cementitious materials (SCMs). In addition to durability properties, the effects of CS on mechanical characteristics and properties of fresh concrete, and microstructure have been studied as well. The outcomes demonstrated that in fresh concrete, CS (up to 7 kg/m3) prompted a decrease in workability and density of fresh concrete without any significant impact on slump loss. The results of hardened concrete evaluation also showed a reduction in either density of hardened concrete or compressive strength. Plus, microstructure analysis showed that incorporation of CS deteriorates both the cement paste and the interfacial transient zone. Eventually, although CS had a negligible impact on electrical resistivity, total water absorption, and chloride diffusivity, it was absolutely effective on permeability of concrete under non-hydro static pressure. In this regard, inclusion of CS drastically reduced the depth of capillary penetration of water in addition to short and long term water absorption. As a case in point, incorporation of 7 kg/m3 of CS decreased the last-mentioned parameters by respectively 60%, 72%, and 40% compared to the reference mixture after 120 days of moist curing.

Cellulose nanofibres (CNF) for sulphate resistance in cement based systems

Cellulose nanofibres (CNF) are employed for the first time to address sulphate penetration and subsequent dimensional change in the cementitious system. Using four different Portland cement based binders, paste and mortar mixtures were prepared to have up to 0.5% dry CNF by volume fraction. After 28 days of moist curing, the specimens were subjected to accelerated sulphate attack for 12 weeks. Unidirectional penetration of sulphate was determined according to a modified ASTM C114 method. Alongside, the change in length was measured as per ASTM C 1012. The results show that CNF visibly reduces the penetration of sulphate ions inside the cementitious system. As well, it effects a marked reduction in the Ettringite produced and the associated expansion. Of particular significance to the construction industry is that at 0.3–0.5%, CNF imparts as much resistance to Type GU Portland cement against sulphate attack, as the specially formulated sulphate resistant cements.

Characterisation of self-healing efficiency of calcium nitrate microcapsules for concrete applications

This study presents characterisation of concrete samples containing 0.75% by cement weight of modified calcium nitrate self-healing microcapsules. The phased array ultrasonic testing method was used to investigate the healing efficiency of calcium nitrate microcapsules in concrete. The method is a novel non-destructive testing technique that is commonly used for detecting the defects in welding. Concrete beams were prepared from the control mix (without microcapsules) and mixes containing 0.75% by weight of cement of calcium nitrate microcapsules. After 28 days of moist curing, the phased array ultrasonic images of all beams were captured before loading, after applying 60% of the ultimate flexural load, and after 3 and 7 days of accelerated healing. Moreover, scanning electron microscopy images taken from fractured surfaces of the beams that were loaded up to failure before healing were compared to those of the beams that were healed for 7 days and loaded up to failure.

Durability and Compressive Strength of High Cement Replacement Ratio Self-Consolidating Concrete

This study examines durability and mechanical properties of sustainable self-consolidating concrete (SCC) in which 80% of the cement is replaced with combinations of recycled industrial by-products including fly ash, silica fume, and ground granulated blast furnace slag (GGBS). The water to binder (w/b) ratio of SCC mixes studies was maintained at 0.36. The study proposes empirical relationships to predict 28-day compressive strengths based on the results of three-day and seven-day compressive strengths. In addition, the chloride penetration resistance of the various sustainable SCC mixes was determined after three days, seven days, and 28 days of moist curing of concrete standards. It was concluded that fly ash, silica fume, and GGBS contribute favorably to enhancing strength development, fresh properties, and durability of SCC in comparison to ordinary Portland cement (OPC). The compressive strength of the sustainable SCC mixes falls within ranges suitable for structural engineering applications. Replacing cement with 15% silica fume produced a 28-day average compressive strength of 95.3 MPa, which is 44.2% higher than the control mix. Replacing cement with 15% or 20% silica fume reduced the chloride ion permeability to very low amounts compared to high permeability in a control mix.