Low Initial Strength Research Articles

Impact of in-situ CO2 injection on natural and accelerated carbonation performance of aerial lime mortar

Aerial lime is a well-known carbonatable binder. To address some limitations of slow carbonation speed and low initial strength, this study proposes an internal carbonation technique for field-casting aerial lime mortar using in-situ CO2 injection. The technique was found to be significantly effective in accelerating the carbonation and strength development of the mortar. For the first 28 days, the mortars mixed with CO2 injection showed 1.25–1.68 times faster carbonation and 1.5–2.3 times higher compressive strength than the mortar mixed without CO2 injection. This improvement can be explained by the internal carbonation effect, which effectively refines the pore structure while providing a nucleation site for subsequent carbonation. The early refinement of the pore structure also increased later carbonation performance under both natural and accelerated conditions.

Development and application of artificial hydraulic lime for Chinese architectural heritage restorations

Lime is commonly employed in the restoration of historic buildings due to its strength properties, which align well with the demands of architectural heritage conservation. However, recent shortages in high-quality limestone raw materials and the commercial inclusion of finely ground limestone powder in hydrated lime powder have led to significant challenges. These include low initial strength, pronounced shrinkage and cracking, and poor resistance to frost. Although natural hydraulic lime (NHL) offers moderate strength, its high cost presents an obstacle to widespread use in architectural heritage restoration. Three types of artificial hydraulic lime (AHL) — AHL1, AHL2, and AHL3 — were prepared with the objective of low cost and easy scalability. These were formulated by incorporating white cement (WC), blast furnace slag powder (BFSP), heavy calcium carbonate powder (HCCP), and industrial-grade white sugar (WS) into industrial-grade hydrated lime powder (IHLP). To align the setting time of the AHLs with the requirements of traditional builders, WS was incorporated as a retarding agent. The addition of WC, BFSP, and HCCP to IHLP resulted in enhancements over IHLP in several key aspects: compressive strength, pore structure post-hardening, dry shrinkage rate, and frost resistance. This approach will enhance the restoration quality of architectural heritage in China, leading to fewer repeated repairs and significant savings in manpower and material costs. Ultimately, AHL2 was applied in the restoration of the Confucius Temple, proving its efficacy and alignment with traditional construction requirements. This research provides valuable theoretical and practical insights for enhancing the preservation of architectural heritage.

Hydration Characteristics of Slag-Ca(OH)2-Al2O3 Binder in a 60 °C Curing Environment with Brine as Mixing Water

Recently, research results on PC-based or alkali-activated slag cement (AASC) using seawater as mixing water have been reported. Unlike seawater, reverse osmosis brine (brine) is waste discharged into the ocean from seawater desalination plants. There is a need to develop new and effective methods of disposing or utilizing brine to reduce marine pollution, protect marine ecosystems, and increase marine plant construction. However, research on cement or concrete using brine as a mixing water is very limited. Brine has almost the same composition as seawater, and the ion concentration is 2–4 times higher. Therefore, it is believed that new methods of using brine can be investigated and developed based on existing research and experimental results on seawater. The effects of brine and aluminum oxide (AO) on activated slag with calcium hydroxide (CH) were investigated for hydration and mechanical properties. 5% and 10% of CH were used, and samples using fresh water (FC) were prepared at the same time for comparison with brine. The slag sample without CH has a low initial (1 and 3d) strength of about 10 MPa for both FC and brine, but increases rapidly from 7d. Incorporation of CH was effective in improving the mechanical performance of FC and brine samples. In addition, the brine sample exhibited higher strength than the FC sample because it formed fewer C3AH6 phases that cause volume instability than the FC sample and affected the hydration promotion of slag particles. And more calcite phases were observed in the brine samples than in the FC samples. Through this study, the possibility of using brine as a building material was confirmed. In addition, the effect of chloride ion adsorption of slag mixed with AO and CH on the physical properties and mechanical performance of the hydration reaction was confirmed.

Impact of curing on the volumetric and mechanical properties of cold bitumen emulsion mix

Cold bitumen emulsion mix (CBEM) is an emerging sustainable material for constructing the base or surface layer of flexible pavements, reducing energy consumption and global warming effects compared to hot mix asphalt. The main challenges associated with CBEM are low initial strength, moisture susceptibility, etc. This is primarily due to water encapsulation. The curing process allows the water to evaporate gradually over time, improving mechanical properties. This study investigates CBEM’s volumetric and mechanical properties under different curing conditions. CBEMs were prepared using low (50 blows) and high (75 blows) compaction efforts and cured at 25, 40, and 55 °C for 1 to 28 days. In volumetric characteristics, the air voids and voids in mineral aggregates decreased slightly with curing, while total binder volume decreased. Effective binder volume and voids filled with binder increased slightly, then decreased. The mechanical properties, i.e., Marshal Stability, Marshal Quotient, Indirect Tensile Strength (ITS), and Moisture Susceptibility parameters like the Indirect Tensile Strength Ratio (ITSR) and Retained Marshal Stability (RMS), were found to improve over time at each curing temperature. Using a high curing temperature further improved the mechanical characteristics of CBEM. The curing process was decelerated in case of CBEM prepared by high compactive efforts compared to CBEM prepared by low compactive efforts. The Michaelis-Menten model can be used to analyze moisture loss growth and the development of mechanical properties over time. The strength-maturity model can be developed by using ITS as strength parameters. There was a strong correlation between all mechanical characteristics and moisture loss.

Effect of Surface Impacting Parameters on Wear Resistance of High Manganese Steel

High manganese steel has always been subjected to pre-hardening treatment before use owing to its low initial strength. Therefore, cast high manganese steel was pre-hardened in this work by surface impacting treatment under different parameters to evaluate its state. The microstructures, hardening characteristics, and wear resistances of the pre-hardened high manganese steel samples were all investigated. The results indicated that increasing the sample temperature, reducing the impact pin size, and increasing the impact times on a single-point can enhance the surface hardening effect to different degrees. Dislocations and deformation twins were produced on the top surface and within a certain depth of test steel under different impacting conditions. The optimal hardening effect of test steel was achieved at a temperature of 300 °C, a pin size of 10 × 10 mm2, and 9 impacts on a single point. The surface hardness of the treated sample reached 542 HV. For friction and wear testing, the best wear resistance was achieved at a temperature of 300 °C, a pin size of 10 × 10 mm2, and 3 impacts on a single point with a surface hardness of 446 HV. Further enhancement in impact hardening effect resulted in microcracking along the surface of test steel. In turn, the induced embrittlement led to the poor wear resistance.

OVERVIEW OF TECHNOLOGIES FOR OBTAINING COLD EMULSION-MINERAL MIXTURES

The use of cold emulsion-mineral mixture (CBEM) instead of hot asphalt concrete mixture (HMA) has several advantages. Benefits include saving materials and reducing energy consumption, protecting the environment and reducing costs. Cold mixture obtained by mixing mineral aggregate with bitumen emulsion. Despite the efforts made over the last few decades to improve and develop CBEM, certain disadvantages remain that make it inferior to HMA, leading to the limitation or minimization of its use. However, the development of CBEM for road construction, reconstruction and maintenance is constantly gaining interest in both the industrial and research sectors of road construction. Researchers in the field of road construction are constantly looking for ways to reduce energy consumption, greenhouse gas emissions and increase cost efficiency. Cold emulsion-mineral mixture is the result of research in this direction during the last few decades. CBEM is a mixture obtained by mixing bitumen emulsion, aggregates and filler at ambient temperature. Using CBEM, it is possible to achieve 95% energy savings compared to the production of HMA. The disadvantages of cold mixture are also obvious. Because the water must evaporate from the bitumen emulsion for the bitumen to adhere to the aggregates, the cold mix may take several weeks to reach its full strength. This can result in lower initial strength and high porosity compared to conventional hot mix asphalt. Also, because of the water in the mix, potential moisture damage and durability are concerns. As a result, CBEM was rarely used as a structural layer of the roof.

A Study on Hydrated Phases of Ternary Blended Binder via Thermal Analysis

Replacing the cement content with alternatives material such as GGBS is a wonderful way to solve the issues of environmental degradation caused by cement manufacture. However, the concrete produced using GGBS has some drawbacks such as lower initial strength and higher dry shrinkage. Thus, the ternary blended binder replacement was proven to improve the properties of concrete due to its synergistic effect. RHA is an agricultural waste achieving broader awareness because of its considerable impact on the microstructural properties as well as improving the strength of the concrete. Therefore, in this study, cement as a primary binder containing high-volume GGBS was prepared with RHA via adiabatic temperature (steam curing) and normal curing conditions. The effects of increasing the amount of RHA pre-treated as replacement level of the primary binder with 5%, 10%, 15%, and 20%, with a constant amount of GGBS (50% of slag) were characterized using thermogravimetric analysis (TGA/DTA). The findings showed that RHA reacted as a filler and can be used as a secondary source of SiO2 in cement containing high-volume GGBS production. The inclusion of 60% replacement of RHA-GGBS improves the CSH gel due to CH consumption with SiO2 which is more prominent in long terms ages.

Influence of Chitin Nanocrystals on the Crystallinity and Mechanical Properties of Poly(hydroxybutyrate) Biopolymer.

This study focuses on the use of pilot-scale produced polyhydroxy butyrate (PHB) biopolymer and chitin nanocrystals (ChNCs) in two different concentrated (1 and 5 wt.%) nanocomposites. The nanocomposites were compounded using a twin-screw extruder and calendered into sheets. The crystallization was studied using polarized optical microscopy and differential scanning calorimetry, the thermal properties were studied using thermogravimetric analysis, the viscosity was studied using a shear rheometer, the mechanical properties were studied using conventional tensile testing, and the morphology of the prepared material was studied using optical microscopy and scanning electron microscopy. The results showed that the addition of ChNCs significantly affected the crystallization of PHB, resulting in slower crystallization, lower overall crystallinity, and smaller crystal size. Furthermore, the addition of ChNCs resulted in increased viscosity in the final formulations. The calendering process resulted in slightly aligned sheets and the nanocomposites with 5 wt.% ChNCs evaluated along the machine direction showed the highest mechanical properties, the strength increased from 24 to 33 MPa, while the transversal direction with lower initial strength at 14 MPa was improved to 21 MPa.

Microstructural Evolution of Cantilever Wire Probe after Touch-Down Fatigue Cycles for Power Semi-Conductor Wafer Testing

As fatigue fracture occurs in the bending area of the wire probe of the probe card owing to fatigue load during the touch-down (T/D) test, the development of wire probe materials with improved fatigue properties according to the wire materials is required. In this study, Tungsten (W), Rhenium-Tungsten (ReW), Beryllium-Copper (BeCu), and P7 (Palladium - Silver - Copper alloy, Pd-Ag-Cu) alloy were used to measure the tensile strength of the cantilever wire which was utilized for testing the electrical property of power semiconductor wafers used in the probe card. Additionally, the fatigue characteristics and microstructure changes of the wire were analyzed according to the T/D fatigue test using a scanning electron microscope, and electron back-scattered diffraction analysis was used for comparative analysis. In W and ReW wire probes with high initial yield strength, the misorientation angle due to grain elongation was smaller than that of P7. Accordingly, the grain deformation due to strain generation was small, whereas in materials with low initial yield strength, the misorientation angle was smaller. However, the amount of strain generated by grain orientation deformation was large. Therefore, under long-term T/D test conditions, it is assumed that ReW, W, and BeCu wire materials, which generate less deformation after long-term use than those with high initial strength, are superior to P7 materials.

The mechanism of hydration reaction of granulated blast furnace slag-steel slag-refining slag-desulfurization gypsum-based clinker-free cementitious materials

In this study, refining slag containing high hydration active component C12A7 was added in GBFS−SS−DG−based clinker−free cementitious material. The optimum was determined by an orthogonal test and the influence of heat treatment was studied. The participation of refined slag makes the compressive strength of 3 days reached 27.4 MPa, 60.6% of that at 56 days, which overcomes the shortcoming of low initial strength of GBFS−SS−DG−based clinker−free cementitious material. Microscopic analysis showed that quantities of ettringite occurred in 3 days. During the hydration, C3AH6 was formed by the hydration reaction of C3A and C12A7 and then reacted with the CS‾H2 to form ettringite which constituted the basic framework. Under the alkaline condition provided by steel slag, SiO4 tetrahedra and AlO4 tetrahedra were constantly dissociated from GBFS, then C–S–H gels and ettringite were further developed, which was corroborated by results of IR and XPS. In middle and late period, amounts of C–S–H gels wrapped AFt crystals and filled the pores, and finally formed a unified composite structure, which was responsible for the high strength of 43.0 MPa at 28 days.

Experimental characterization of quaternary blended mortar exposed to marine environment using mechanical strength, corrosion resistance and chemical composition

The durability of concrete is significantly influenced by its binder composition, especially in the presence of aggressive chemical environment. This paper represents a study on the strength, durability, and corrosion resistance of quaternary blended mortar made with Portland pozzolana cement (PPC), ground granulated blast furnace slag (GGBS) and rice husk ash (RHA) exposed to marine environment. Binary blended concrete mix using GGBS and RHA as partial replacement for cement is already well established. Previous research reports several shortcomings in using binary blended and ternary mix including low initial strength and increasing shrinkage strains with increasing percentages of GGBS, silica fume and RHA as partial substitutes for cement. Hence, this study is focused on overcoming the limitations of binary and ternary blended mixes by implementing a quaternary blended mix using GGBS and RHA to partially replace cement. This quaternary blended cementitious system is optimized based on its mortar compressive strength, determined by varying the percentages of GGBS and RHA as substitute for cement. These optimized quaternary mortar specimens are moist-cured for 28 days and then exposed to an artificially prepared marine environment for 180 days. The optimized quaternary blended mortar specimens show improved mechanical strengths, both compressive and flexural. These specimens also exhibit enhanced resistance to chloride penetration, corrosion, and water absorption compared to the control mix after 28 days of water curing. A quaternary blended mortar mix prepared with 70% PPC, 20% GGBS, and 10% RHA exhibits the maximum mechanical strength, resistance to chloride penetration, and corrosion, mass loss and water absorption upon exposure to marine environment up to a period of 180 days. Mineralogical analyses using X-ray diffraction (XRD), chemical bond analyses using Fourier Transform Infra-Red (FTIR) spectroscopy, and microanalyses using scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray spectroscopy (EDS) are implemented to determine the effects of marine environment exposure on the different mixes. The findings are then used to corroborate the observations from the specimen scale mechanical and chemical characterizations.

Design Method and Evaluation Criteria on Gyratory Compaction Based Cold-Mixed and Cold-Laid Recycled Asphalt Mixture

Cold-mixed recycled asphalt mixture is widely used due to the advantages of good eco-friendliness, resource conservation, and convenient construction. In order to further improve the mixing ratio design theory of cold-mixed recycled mixture, this paper has presented the research on design method and evaluation criteria of cold-mixed and cold-laid recycled asphalt mixture based on gyratory compaction. Research has shown that fine aggregate and mineral powder adhere to asphalt and exist in the form of agglomeration in the Reclaim Asphalt Pavement (RAP), which will cause the gradation of the milling plan material to decay after extraction. According to the viscosity characteristics of cold mixed asphalt, it is recommended that the mixing temperature of the mixture should be greater than 25°C, the compaction of cold-mixed recycled mixtures is easier to achieve by using gyratory compaction method. The paper proposes a test method to determine the optimal asphalt content based on initial strength and sweep test, and proposes a test method for controlling the strength of the mixture by the number of compactions and the forming temperature, establishes evaluation system of initial strength and final strength of cold-mixed recycled mixture, and corrects the evaluation method of high temperature stability and water stability of cold-mixed recycled mixture. The results show that the cold-mixed recycled mixture has low initial strength, insufficient high-temperature stability and water stability. With the volatilization of the diluent, the strength, high temperature stability and water stability of the mixture have been significantly improved.

Adhesive Reliability Study at the Encapsulant/Backsheet Interface of Solar Modules for Various Ethylene-Vinyl Acetate Copolymer White Films

White EVA film has recently been widely applied between the solar cells and the backsheet to improve the light reflection and gain more power. The peel strength between EVA layer and backsheet may decrease in damp heat environments. The decline in peel strength may vary for different EVA films as well as different match with backsheets. In this work, the weather resistance performance of four different white EVA films were comparatively studied with four different backsheets. Peel strength before and after the damp heat test for 1000h and 1500h was measured. For the interface with low initial peel strength, increase in bonding force was observed after the damp heat test. For the interface with high initial peel strength, degradation in bonding force may probably occur. These results suggest that a higher initial performance cannot always ensure a higher performance after degradation.

Lime/pozzolan/geopolymer systems: Performance in pastes and mortars

Use of lime as construction material is limited mainly by low initial strength. These properties can be improved by adding pozzolanic materials, but the evolution of the reaction usually needs older ages than 7 days. Alkali-activated materials, or geopolymers, are good-performance materials that can be produced with residual waste. The combination of traditional and new materials can lead to new uses of lime mortars. This paper studies a lime/pozzolan and geopolymer mixture. The chosen pozzolan is fluid catalytic cracking catalyst residue (FCC), a material employed as a precursor in alkali-activated material. FCC is activated by two activators: a mixture of NaOH and waterglass; a mixture of NaOH and rice husk ash (RHA). The new materials were studied in microstructure and mechanical behaviour terms. The results demonstrated that lime/pozzolan/geopolymer obtained superior compressive strengths after 1 curing day to that obtained for the corresponding lime/pozzolan mortar after 90 days. An improvement in compressive strength of around 145% was achieved for the mortar with 40% geopolymer compared to the mortar with only lime/pozzolan at 28 curing days.

Mechanical behavior of hydroxyapatite-poly(lactic acid) hybrid porous scaffold

Although autologous bone is currently used for repairing bone defects, this method is highly invasive and poses a heavy burden on patients. Thus, the use of artificial bones has been expected. Among the artificial bone materials, bioactive hydroxyapatite (HA) has been attracting much attention. In this research, in order to overcome the problem such as low initial strength of artificial bone after implantation, poly(lactic acid) (PLA) was coated on HA unidirectional porous body prepared by freeze-casting method. In order to investigate the PLA coating method that most effectively improves the mechanical properties, the coating state of PLA was observed and the compression test was performed. As a result of the compression test of the HA-PLA composite porous body, Young’s modulus and compressive strength were improved by 79% and 184% respectively at maximum. Furthermore, acoustic emission (AE) measurement was conducted to investigate the fracture behavior during the compression test, classifying the main fracture of HA and HA-PLA porous body as shear fracture.

Experimental and analytical evaluation of the redundancy of repurposed fracture-critical railroad-flatcars

Previous research focused on the development of guidelines to load rate highway bridges constructed out of repurposed railroad flatcars (RRFCs). Those guidelines were based on field testing and finite element analysis conducted on existing RRFC bridges both in the field and in the lab. However, load rating is only one of the issues related to RRFCs as the main components are often classified as fracture critical members (FCMs) since there are only two flatcars in the cross section in most instances. Classifying the individual RRFCs as FCMs requires a rigorous hands-on inspection as per the Code of Federal Regulations, which greatly increases the long-term costs associated with these structures. Hence, while they are attractive to many owners due to their low initial costs and considerable strength, long-term costs due to inspection have deterred some owners from utilizing this viable and renewable alternative for low-volume applications. This paper presents the results of laboratory testing and non-linear finite element analysis of a railroad flatcar bridge specimen constructed with a composite reinforced concrete deck. The results confirm that RRFCs have considerable reserve strength and adequate load redundancy in a severely faulted state and need not be classified as FCMs if certain requirements are met. The paper also presents recommendations for load redistribution factors between primary members of RRFCs obtained through the experimental and verified by numerical studies.

Fundamental performance investigation on reactive liquid asphalt

Low initial strength, slow strength increase, slow curing, high temperature susceptibility, poor water damage resistance, and poor storage stability are the major shortcomings of traditional cold mix asphalt (CMA). Unlike the traditional CMA, reactive liquid asphalt (RLA) was produced to overcome the weaknesses in this study. Its optimal ingredient mix, which includes silane coupling agents (SCA), asphalt modifiers, reactive solvents (RS), and curing agents (CA) was determined according to the single factor and orthogonal experimental results in the laboratory. The performance of the resulting RLA was systematically evaluated. The fundamental properties proved favorable, which were characterized by penetration of 5 mm, ductility of 49 cm and softening point of 70 °C, the dynamical shear rheology (DSR) and bending beam rheology (BBR) results showed that its performance grading could reach PG70-22, indicating satisfactory for most regions in the world. The adhesion between RLA and coarse aggregate results suggested that the stripping risk was significantly reduced. In addition, the satisfied compatibility and performance of RLA were revealed by analyzing scanning electron microscopy (SEM) and infrared spectral analysis (IR) results.

Emulsified cold recycled mixtures using cement kiln dust and coal waste ash-mechanical-environmental impacts

Cold recycling is a widely recommended asphalt pavement rehabilitation technology with potentially significant economic and environmental benefits. One of the advantages of cold recycling is that its operations are performed at ambient temperature. However, there are still some concerns regarding the use of emulsified cold recycled mixtures (ECRMs). These pavements are susceptible to problems such as raveling, stripping, low initial strength, and long curing time, which are often countered by the use of additives. This study examined the mechanical outcomes and environmental implications of using cement kiln dust (CKD), which is a byproduct of cement production plant, and coal waste ash (CWA), which is obtained by igniting coal waste, in ECRMs as additives. The effects were compared with the additive-free or reference mixture and the mixtures with 1% and 2% cement content. To evaluate the mechanical properties, Marshall stability, indirect tensile strength and moisture susceptibility tests were performed on the specimens of different ages at different temperatures. Environmental impact was assessed using the modified toxicity characteristic leaching procedure (MTCLP) test. Finally an economical-environmental analysis was performed on designed pavements with each type of ECRM. The results showed that the combined use of CKD and CWA improved the mechanical properties, especially after prolonged curing periods. In some cases, this improvement was even greater than the improvement resulting from the addition of cement. The results of the MTCLP test showed that even after five extractions, the concentration of heavy metals in the leachate of CKD- and CWA-containing mixtures remained below the regulatory levels. Overall, it was found that using CKD and CWA as additives in ECRMs had remarkable economical and environmental benefits, especially if they are employed together.

Compressive Strength of Post Fire Exposed Concrete Column Wrapped with Fiber Reinforced Polymer

In this study, behaviour of reinforced concrete columns strengthened using fiber reinforced polymer (FRP; glass fiber and carbon fiber) after fire exposure are discussed. After being exposed to fire as high as 720 o C for 180 minutes, the specimens showed concrete and reinforcement strength degradation, even though there was no carbonation. It was found that specimens wrapped by carbon fiber showed better compressive strength but less ductility compared to specimens wrapped by glass fiber. It was also found that the low initial compressive strength did not decrease FRP confinement effectiveness. Increase of wrapped concrete com­pressive strength was evident despite the low initial strength (<17 MPa). Strength esti­mation using ACI 440.2R-08 formula, which is originally for wrapped plain concrete without fire heat exposure, underestimated the compressive strength. In the proposed formula, the initial compressive strength (f’ co ) should be adjusted by considering the modulus elasticity and strain limitation to have more precise estimation.

Performance Analysis of a Cold Asphalt Concrete Binder Course Containing High-Calcium Fly Ash Utilizing Waste Material

It has been established that cold bituminous emulsion mixtures (CBEMs) have a comparatively low initial strength in comparison to hot mix asphalt (HMA), however its superior performance with regard to carbon emissions, is a significant driver regarding its manufacture. In this research, high calcium fly ash (HCFA) together with a fluid catalytic cracking catalyst (FCC) - a rich silica-alumina waste material - have been incorporated to develop a new cold asphalt concrete binder course (CACB) bituminous emulsion mixture. HCFA was used as a substitute for traditional limestone filler while FCC was the additive used to activate the HCFA. The mixtures’ performance was assessed using the indirect tensile stiffness modulus test (ITSM), assessment of resistance against permanent deformation, temperature and water sensitivity tests. Surface morphology was tested using a scanning electron microscopy (SEM). A considerable improvement was identified by the ITSM test in addition to a substantial enhancement in rutting resistance, temperature susceptibility and water sensitivity. It was also established that the addition of FCC to CACB mixtures was found to improve early strength as well as long-term strength, rutting resistance, temperature sensitivity and durability.