Decrease In Flexural Strength Research Articles

Hybridization Effects on Bending and Interlaminar Shear Strength of Composite Laminates.

Fiber-reinforced composites are gradually replacing the traditional materials in many engineering applications. However, for many applications these materials are still unsuitable, due to their lack of toughness. In this context, hybridization is a promising strategy in which two or more types of fiber are combined to obtain a better balance of mechanical properties compared to non-hybrid composites. Therefore, the main goal of this work is to study the hybridization effect on the static performance and interlaminar shear strength. For this purpose, carbon, glass, and Kevlar fibers were used and combined in different proportions. It was possible to conclude that there is an ideal value of fiber content to maximize both properties and, depending on the type of fiber, they should be placed specifically on the compression or tensile side. For example, for composites involving carbon and glass fibers the latter must be placed on the compression side, and for a value of 17% by weight the flexural strength decreases by only 2.8% and the bending modulus by around 19.8%. On the other hand, when Kevlar fibers are combined with glass or carbon fibers, the Kevlar ones must always be placed on the tensile side and with an ideal value of 13% by weight.

The influence of yttria content on the microstructure, phase stability and mechanical properties of dental zirconia

A bstract The purpose of this study was to fully realize the clinical plausibility of a newly introduced yttria gradient monolithic multilayer dental zirconia and the current indication range for dental zirconia; hence, an investigation leading to a comprehensive understanding of the effect of yttria content on the properties of zirconia was undertaken. Each layer from a yttria gradient monolithic multilayer zirconia system with two types (esthetic and functional types, Meiying Zirconia, UPCERA, China) was selected for investigation of its chemical composition by X-ray fluorescence. Layers with yttria content interval of about 0.4 mol%-0.5 mol% were chosen for subsequent testing. Their phase fractions, grain sizes, low-temperature degradation (LTD) resistance, coefficient of thermal expansion (CTE), and mechanical properties were characterized. The yttria content from the occlusal to the gingival region was from 5 mol% to 4.1 mol% and 4.7 mol% to 3.2 mol% for esthetic type and functional type, respectively. Ultimately, we investigated the selected five yttria content layers, 5Y, 4.5Y, 4Y, 3.6Y, and 3.2Y. With increased yttria content, increasing cubic phase fractions (from 25.86 wt% to 58.53 wt%) and mean grain sizes (from 0.31 μm to 0.72 μm) were detected; monoclinic content after LTD decreased; and there was a decreasing tendency for CTE, although no statistically significant difference was found ( F = 2.43, p = 0.117). In addition, yttria dopant showed no effect on elastic modulus ( F = 2.43, p = 0.464) but slightly increased hardness ( F = 4.10, p = 0.014). However, there were notable decreases in fracture toughness ( F = 227.58, p < 0.001), biaxial flexural ( F = 52.31, p < 0.001), and fatigue strength ( F = 56.52, p < 0.001). The percentages of strength degradation from monotonic to fatigue tests were about 33%–40%, independent of yttria doping ( F = 1.82, p = 0.136).

Biostability of binder-free wood and plant plastics protected with antiseptics

Introduction. Agriculture produces a lot of plant and food waste that is highly biodegradable. In order to recycle this waste and use it in the production of new materials, we need to find effective ways to increase their resistance to biodegradation. We aimed to study the biostability of binder-free wood and plant plastics, as well as to find an optimal method of their antiseptic protection.&#x0D; Study objects and methods. Our objects of study were binder-free plastics based on sawdust, wheat and millet husks. To determine their biostability, we exposed them in active soil for 21 days and analyzed their physical and mechanical properties. Also, we examined the effects of several methods of antiseptic treatment on the samples’ strength, water resistance, and biodegradation.&#x0D; Results and discussion. All the wood- and plant-based samples showed low biostability. Exposure in active soil caused significant morphological and structural changes, as well as impaired the samples’ physical and mechanical properties, especially those of the plant-based plastics. Their resistance to biodegradation was significantly determined by the type of filler or antiseptic, as well as by the method of antiseptic administration. Whether added to the press mixture or applied to the surface, the antiseptics changed the samples’ physical and mechanical properties. Among the antiseptics used, copper sulfate showed the best effect when introduced directly into the sawdust press mixture. It ensured the lowest decrease in flexural strength, but increased hardness, water absorption, and swelling. The wheat- and millet-based plastics protected with copper sulfate showed an increase in strength indicators, but lower water resistance.&#x0D; Conclusion. The antiseptic protection of binder-free wood and plant plastics affects a number of their physical and mechanical properties and therefore should take into account the expected conditions for their performance.

Assessing the properties of Poly(dicyclopentadiene) reinforced with discontinuous carbon fibers

Ring-opening metathesis polymers (ROMPs) have remarkable toughness usually failing in a ductile rather than brittle manner. Despite these advantages, these resins have rarely been evaluated in composite materials. We investigated composites of milled carbon fiber and poly(dicyclopentadiene) (pDCPD), a common and inexpensive ROMP polymer. We observed that 10 wt% fibers gave significant increases in tensile modulus (137%), compressive modulus (34%), and fracture toughness (54%) with significant decreases in tensile (42%) and flexural yield strength (46%). Compressive yield strength, ultimate tensile strength, and flexural modulus remained about the same as the unfilled resin. The increases in modulus were well fit by the rule of mixtures for randomly distributed fibers even though microcomputed tomography data showed local regions of anisotropy due to stress applied during sample fabrication. Decreases in tensile and flexural yield were possibly due to weak interfacial strength arising from a lack of surface treatment on the carbon fiber.

Mechanical properties of carbon/glass fiber reinforced polymer plates with sandwich structure exposed to freezing-thawing environment: Effects of water immersion, bending loading and fiber hybrid mode

In this article, two kinds of carbon/glass fiber hybrid rod with the sandwich structures were designed and developed through the pultrusion technology, including the fiber random hybrid (RH) mode with multi-layer sandwich structure and fiber core-shell hybrid (CH) mode with single-layer sandwich structure. The hybrid sandwich-structure plates were prepared from the rod and immersed in bending loading, temperature alternating and sustained water immersion as long as 360 days. The effect of fiber hybrid mode/sandwich structure on the degradation mechanism of mechanical properties was revealed through the digital image correlation and thermogravimetric analysis. Through the fiber hybrid design, the strength improvement percentages of RH plates with multi-layer sandwich structure were up to ∼50% (tensile strength), 30 ∼ 40% (flexural strength) and 18% (in-plane shear strength) compared to CH plates with single-layer sandwich structure. Higher bending loading level brought about the decrease of flexural strength and in-plane shear strength close to 18% and 19%, respectively. During the immersion, microcracks or microvoids formed and expanded in the resin tensile area under the bending loading and water diffusion, leading to the uncoordinated stress concentration for single-layer sandwich-structure CH plate. By uniformly dispersing carbon fibers into glass fibers, the uneven interface stress concentration can be effectively alleviated for multi-layer sandwich-structure RH plates. The comparison of mechanical properties with the others’ work showed the interface shear strength was more sensitive to the bending loading and immersion temperature. The long-term life prediction showed the maximum increase percentages of mechanical properties of multi-layer sandwich structure were 435.4% (tensile strength) and 149.2% (flexural strength) and 110.7–114.2% (shear strength) compared to the single-layer sandwich structure.

Evaluation of the effects of different concentrations of bleaching agents on flexural strength and microhardness of VITA ENAMIC

Considering the studies on the effects of bleaching materials on properties of dental materials, The aims of this in vitro study were to evaluate the effects of two different concentrations of bleaching agents on flexural strength and microhardness of VITA ENAMIC. In this experimental in vitro study, 30 rectangular-shaped specimens (2 mm width × 2 mm height × 12 mm length) for flexural strength and 30 specimens (5 mm width × 5 mm length × 2 mm height) for microhardness tests were prepared from VITA ENAMIC blocks 12 × 14 × 18 mm. The specimens were polished using silicon-carbide sandpapers 400, 600, 800, 1200, 2000 under flow of water for 60 s each. The prepared samples for flexural strength and microhardness were divided into 3 subgroups (n = 10): control group (C), samples bleached using Opalescence PF 15% (B15), and samples bleached with Opalescence Xtra Boost 40% (B40). Flexural strength measurement was done using a universal testing machine, and microhardness test was done using Vickers. Data were analyzed using analysis of variance and post hoc tests and P < 0.05 was considered significant. The mean microhardness values of C, B15, and B40 groups were 255.46 ± 3.02, 249.86 ± 4.18, and 235.53 ± 4.61 kgf/mm2. Opalescence PF 15% and Opalescence Xtra Boost 40% affected microhardness of ENAMIC significantly (P < 0.05). The mean flexural strength values of C, B15, and B40 groups were 155.26 ± 16.13, 142.14 ± 11.52, and 133.39 ± 16.13 MPa. A significant decrease in flexural strength was found between the C and B40 groups (P = 0.007). However, the difference between flexural strength of the C and B15 groups was not significant (P > 0.05). Our study showed that both concentrations of bleaching agents can affect microhardness of ENAMIC. Moreover, hydrogen peroxide 40% has a negative effect on the flexural strength of ENAMIC.

Effect of trass substitution in sand on the compressive and flexure strength of concrete

The existence of limitations in the supply of sand as a concrete material requires an alternative. On the other hand, the potential trass in Rembang is quite abundant and has not been utilized optimally. This study utilizes the potential of trass ex. Rembang is a substitution of sand in concrete with compressive and flexural strength as test parameters. Concrete with a design quality of 33 MPa is made from the split, cement, water, and sand substituted with trass 0,20,40,50,60,80, and 100% of the weight of sand in cylinders 15/30 cm and beams 15x15x60 cm. The concrete was treated with wet burlap and tested at the 3, 7, 14, 28, and 90 days in compression also 7 and 28 days in flexure. The test results show that the presence of trass in the concrete reduces the concrete compressive strength by 17% until 42% of the concrete compressive strength without trass. Moreover, the flexural strength decreases by 7% to 23%. Concrete using a fine aggregate in the form of trass (100% trass) has increased compressive strength with increasing age of the concrete, but with a compressive strength of 36% lower than the compressive strength of concrete with sand as the fine aggregate.

Mechanical and Rheological Properties of Bamboo Pulp Fiber Reinforced High Density Polyethylene Composites: Influence of Nano CaCO3 Treatment and Manufacturing Process with Different Pressure Ratings

In order to investigate the effect of the relative motion of nano CaCO3 reinforced bamboo pulp fiber (BPF)/HDPE composite components on the mechanical performance, a comparative study was performed. BPF was treated by nano CaCO3 blending (BM) and impregnation modification (IM) technology. The composites were produced using hot press (HPMP), extrusion (EMP) and injection molding process (IMP). The physical morphology of BPF was similar at different manufacturing processes. Compared to the samples manufactured by HPMP, a decrease in the (specific) flexural strength of BPF/HDPE composites and an increase in those of composites treated by nano CaCO3 manufactured by EMP and IMP were observed. The injection molded composites exhibited the best values in the (specific) impact strength, (specific) tensile properties. IM had a greater effect on the rheological behavior of the composites than BM, and nano CaCO3 treatment most effectively affected the performance of the extrusion molded composites.

Study of a thermally enhanced mortar incorporating phase change materials for overheating reduction in buildings

The use of thermal energy storage systems incorporating Phase Change Materials (PCM) as passive thermal regulators, in innovative buildings’ applications is an increasing trend and promising strategy for maintaining indoor thermal comfort while promoting buildings’ energy efficiency in a sustainable way. Incorporating PCM into mortars enhances their thermal properties but modifies physical and mechanical characteristics. This paper presents an experimental research on the microstructural, mechanical, and thermal properties of innovative cementitious mortars incorporating two different microencapsulated PCMs, targeted for low thermal mass constructions located in warm climates.The characterization was developed in three steps: microstructural evaluation using scanning electron microscopy; physical and mechanical characterization by workability, density as well as compressive and flexural strength tests; and thermal characterization through enthalpy-temperature curves, determined with differential scanning calorimetry, and the assessment of real case application to evaluate the impact over the thermal behaviour of a lightweight constructive solution with the developed mortars as inner finishing layer using the hot box heat flux metre method at steady-state conditions. Results revealed an expressive decrease in flexural and compressive strength; significant loss of latent heat capacity and variations of onset and peak melting temperatures were observed; good correlation between thermal conductivity and mean specimen temperatures were attained for the lightweight opaque building solution tested with the two different PCMs, for temperatures below and above the phase change transition zone.

Evaluation of New Hollow Sleeve Composites for Direct Post-Core Construction.

The preset shape and diameter of a prefabricated FRC post rarely follows the anatomy of the root canal. To solve this problem, a new hollow sleeve composite (HSC) system for post-core construction was developed and characterized. A woven fiber was impregnated with two types of resins: Bis-GMA or PMMA, and rolled into cylinders with outer diameter of 2 mm and two different inner diameters, namely 1.2 or 1.5 mm. The commercial i-TFC system was used as a control. Dual-cure resin composite was injected into these sleeves. Additionally, conventional solid fiber post was used as the inner part of the sleeve. The three-point bending test was used to measure the mechanical properties of the specimens and the fracture surface was examined using an electron microscope (SEM). The HSC (1.5 mm, Bis-GMA) revealed a statistically similar flexural modulus but higher flexural strength (437 MPa) compared to i-TFC (239 MPa; ANOVA, p < 0.05). When a fiber post was added inside, all values had a tendency to increase. After hydrothermal accelerated aging, the majority of specimens showed a significant (p < 0.05) decrease in flexural strength and modulus. SEM fracture analysis confirmed that the delamination occurred at the interface between the outer and inner materials. The HSC system provided flexibility but still high mechanical values compared to the commercial system. Thus, this system might offer an alternative practical option for direct post-core construction.

Recycled Precast Concrete Kerbs and Paving Blocks, a Technically Viable Option for Footways.

The linear economy paradigm in place to date has to be seriously challenged to give way to a new school of thought known as the circular economy. In this research work, precast kerbs and paving blocks made with recycled concrete (RACC-mixture) bearing 50 wt% mixed recycled aggregate (masonry content of 33%) and an eco-efficient cementitious material as 25 wt% conventional binder replacement were evaluated to assess their intrinsic potential to replace traditional raw materials, in keeping with circular economy criteria. Therefore, precast products were subjected to mechanical strength, durability and microstructure tests and were compared to conventional concrete units (CC-mixture and commercially available precast elements). Although a class demotion was observed for water absorption and some decreases in flexural strength (26%), splitting tensile strength (12.8%) and electrical resistivity (45%) and a lower class water absorption were registered, and the recycled mixture also exhibited a greater performance in terms of compressive strength (6%), a better abrasion resistance classification and a comparable porosity and microstructure, which ensures a good concrete durability. In any case, the results showed that precast pieces were European standard-compliant, thus supporting the viability of the mixed recycled aggregates and eco-efficient cementitious replacement in footways.

Effect of TEA·H3PO4 and TEA·C18H30O3S on the mechanical properties and hydration characteristics of cement paste

In this study, TEA·H3PO4 (TP) and TEA·C18H30O3S (TDS) have been used as organic admixtures in cementitious materials. Mortar specimens with different TP and TDS dosages were subjected to mechanical, setting time, hydration degree, isothermal calorimeter tests, as well as to XRD, TG, SEM and MIP analyses. Results show that less than 0.10% TP and 0.05% TDS shorten the initial setting time, while more than 0.50% TDS can lead to a retarding effect in mortar specimens. TP is beneficial to increase the early age strength, but a sharp decrease in both compressive and flexural strengths is found when TDS is introduced. The XRD and TG analyses indicate that the introduction of TDS brings more generation of the portlandite (CH), ettringite (AFt), and monosulfate (AFm), whereas TP leads to the reduction of CH content in the cement pastes. Moreover, the SEM observations reveal that the decline in strength may result from the air-entraining effect caused by the incorporation of TDS which increase the amount and size of hydration pores, and the variation of mechanical properties of mortar specimens with TP is closely linked to the size of CH generated in mortar specimens.

PA6/PA66/talc composite: Effect of reprocessing on the structure and properties

AbstractIn this study the effect of repeated injection molding cycles on the structure and properties of polyamide 6/polyamide 66/talc (PA6/PA66/talc ‐ 35/35/30) composite was investigated for samples subjected to one, four, and seven processing cycles. Their morphology (scanning electron microscopy), structure (Fourier transform infrared spectroscopy), melt viscosity (melt flow index [MFI]), mechanical (tensile, flexural, impact, and fatigue tests), and thermal properties (differential scanning calorimetry and thermogravimetric analysis tests) were analyzed. The increase in MFI value and the decrease in the maximum decomposition temperature of PA6, observed by TG analysis, for samples subjected to seven processing cycles, indicated a possible reduction in molar mass of the PA6/PA66 matrix. These samples presented a decrease in degree of crystallinity of PA6 and PA66, which was more pronounced for PA6. The reprocessing of the composite did not present changes in the mechanical properties up to the fourth processing cycle, except for fatigue life which presented a 59% reduction. Samples subjected to seven processing cycles presented a decrease in tensile and flexural strength as well as in tensile and flexural modulus. Charpy impact strength of the samples did not significantly change upon reprocessing. The micrographs of the fatigue fractured surfaces indicated that the weak talc‐matrix interaction and talc‐matrix debonding became more evident with increasing processing cycles.

The interfacial microstructure and fracture toughness of W/Ta multilayer composites

The application of tungsten (W) material is limited due to its intrinsic brittleness at low temperature. W-based multilayer composites are one of the solutions to improve the fracture toughness of W. In this study, a series of tungsten/tantalum (W/Ta) multilayer composites are prepared by diffusion bonding. The interfacial microstructure and fracture toughness under different deformation modes are investigated. It has been found that the flexural strength and fracture toughness loading perpendicular to the W/Ta interface are significantly higher than that loading parallel to the interface. The composites bonded at 1000 °C exhibits the highest flexural strength and fracture toughness. Both the flexural strength and fracture toughness decrease as bonding temperature increases. The decrease of flexural strength is due to recovery and recrystallization of the W layers. The decrease of fracture toughness is mainly attributed to the changes of the interfacial microstructure and fracture mechanism. For the composites bonded at 1000 °C, plastic deformation of the Ta layer and interfacial debonding are the main mechanisms for energy dissipation during crack propagation. As the bonding temperature increases, the decomposition of oxide scale and dynamic recrystallization occur at the vicinity of the W/Ta interface. A layer of fine recrystallization grains is developed at the W/Ta interface when the bonding temperature is higher than 1300 °C. As the interfacial bonding defects decreases, the interfacial bonding strength increases. Therefore, the interfacial debonding is inhibited in the composites bonded at a temperature higher than 1200 °C, instead, multiple tunnel micro-cracks appear in the W layers.

Influence of Firing Temperature on Phase Composition and Color Properties of Ceramic Tile Bodies.

This study is focused on the behavior of the cream-firing clays from Opoczno region (Poland). The ceramic masses on which tests were carried out consisted of cream-firingBorkowice clay and dolomite in two different grain sizes as an additive that changes the color of ceramic materials. Test samples were prepared by plastic method and fired at range of 1100–1240 °C. Phase composition of theinvestigated materials was characterized by XRD method with quantitive analysis of the amorphous phase determined by the Retvield technique. Color properties of the surface of the obtained ceramic materials were determined in CIE-Lab color space. The phase composition of the obtained ceramics depends on the firing temperature. The color of the surface of the ceramic materials also depends on the firing temperature. There was a tendency to decrease the brightness, decrease the blue shade, and increase the yellow shade of the surface of materials with increasing the temperature. The conducted tests allowed to conclude that the color of ceramic materials depends on their phase composition. The most important role in the formation of color correspond to the amorphous phase, formed during the process. The lower content of the amorphous phase in the material allows to obtain brighter products with a lower proportion of yellow, and therefore closer to white. Moreover, following tests were carried out: total water absorption, total open porosity, linear shrinkage, and flexural strength. With increasing the temperature, total water absorption and total open porosity decrease, and total linear shrinkage increases due to the progressive sintering process. Flexural strength increases with the increase of the firing temperature for materials consisting of Borkowice clay. The addition of dolomite introduced new pores into the material, which resulted in an increase in flexural strength at lower firing temperatures and a decrease in flexural strength at higher firing temperatures.

Properties and Strength Prediction Modeling of Green Mortar with Brick Powder Subjected to a Short-Term Thermal Shock at Elevated Temperatures.

The cement industry is responsible for 8% of global CO2 production. Therefore, a clear trend has been observed recently to replace to some extent the main binder of cement composites with environmentally friendly or recycled materials with a lower carbon footprint. This paper presents the effect of brick powder (BP) on the physico-chemical and mechanical properties of cement mortars. The effect of a short-term thermal shock on morphology and strength properties of green mortars was investigated. BP addition caused increase in porosity and decrease in compressive and flexural strength of mortars. The best results were obtained for samples with 5% wt. BP addition. Above this addition the strength decreased. The mechanical performance of the samples subjected to thermal loading increased compared to the reference samples, which is the result of a process called as the “internal autoclaving”. The BP addition positively affects the linear shrinkage, leading to its reduction. The lowest linear shrinkage value was achieved by the mortar with the highest BP addition. An intelligent modeling approach for the prediction of strength characteristics, depending on the ultrasonic pulse velocity (UPV) is also presented. To solve the model problem, a supervised machine-learning algorithm in the form of an SVM (support vector machines) regression approach was implemented in this paper. The results indicate that BP can be used as a cement replacement in cement mortars in limited amounts. The amount of the additive should be moderate and tuned to the features that mortars should have.

3D printable concrete with natural and recycled coarse aggregates: Rheological, mechanical and shrinkage behaviour

In the current study, we examine the effect of using natural and recycled coarse aggregates in designing 3D printable concrete. We assessed the rheological behaviourusing a dynamic shear rheometer, and it was observed that the addition of coarse aggregates significantly decreased the yield stress and marginally lowered the plastic viscosity. This was attributed to the increase in the paste and water film thickness with the addition of larger aggregates. Therefore, a reduction in the superplasticizer dosage is required to obtain coarse aggregate mixtures with similar yield stress and buildability to the control mixture. The mechanical properties were evaluated by using beam and cube samples cut out from printed wall elements. A marginal decrease in compression and flexural strength was observed for both the mixtures with natural and recycled coarse aggregates. The total and autogenous shrinkage assessment was performed using mould cast prismatic specimens, while the shrinkage cracking potential was evaluated using the restrained ring test. The coarse aggregate mixtures showed lower total and autogenous shrinkage. Notably, the addition of the saturated recycled aggregates significantly lowered the autogenous shrinkage, possibly due to internal curing. As a result, a relatively lower strain rate factor and slower development of tensile stresses occurred in the restrained shrinkage test, increasing the cracking age for the coarse aggregate mixtures. The current study, therefore, shows good potential for using natural and recycled coarse aggregates in 3D printable concrete.

Physical Properties and Non-Isothermal Crystallisation Kinetics of Primary Mechanically Recycled Poly(l-lactic acid) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

The physical properties and non-isothermal melt- and cold-crystallisation kinetics of poly (l-lactic acid) (PLLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biobased polymers reprocessed by mechanical milling of moulded specimens and followed injection moulding with up to seven recycling cycles are investigated. Non-isothermal crystallisation kinetics are evaluated by the half-time of crystallisation and a procedure based on the mathematical treatment of DSC cumulative crystallisation curves at their inflection point (Kratochvil-Kelnar method). Thermomechanical recycling of PLLA raised structural changes that resulted in an increase in melt flow properties by up to six times, a decrease in the thermal stability by up to 80 °C, a reduction in the melt half-time crystallisation by up to about 40%, an increase in the melt crystallisation start temperature, and an increase in the maximum melt crystallisation rate (up to 2.7 times). Furthermore, reprocessing after the first recycling cycle caused the elimination of cold crystallisation when cooling at a slow rate. These structural changes also lowered the cold crystallisation temperature without impacting the maximum cold crystallisation rate. The structural changes of reprocessed PHBV had no significant effect on the non-isothermal crystallisation kinetics of this material. Additionally, the thermomechanical behaviour of reprocessed PHBV indicates that the technological waste of this biopolymer is suitable for recycling as a reusable additive to the virgin polymer matrix. In the case of reprocessed PLLA, on the other hand, a significant decrease in tensile and flexural strength (by 22% and 46%, respectively) was detected, which reflected changes within the biobased polymer structure. Apart from the elastic modulus, all the other thermomechanical properties of PLLA dropped down with an increasing level of recycling.

The role of carbonated steel slag on mechanical performance of ultra-high performance concrete containing coarse aggregates

Carbonated fine steel slag (CSS) can be used as supplementary cementitious materials (SCM) to enhance the sustainability of ultra-high performance concrete (UHPC). However, the role of CSS on the mechanical performance of UHPC containing coarse aggregates (UHPC-CA) has not been well understood. Here, the influence of cement substitution by CSS on the hydration products, microstructure, mesoscale fracture characteristics and macroscopic strength of UHPC-CA is investigated. Results reveal that the C-S-H content in UHPC increases with the increase of CSS substitution up to 15%. Replacement of cement by CSS results in a more porous interfacial transition zone (ITZ), consequently, a lower mechanical contribution from CA. Both the compressive and the flexural strength decrease with the increase of CSS substitution, and the negative effect is rather limited till 30% CSS substitution. Moreover, due to a more porous ITZ at a higher cement substitution, the ratio of flexural to compressive strength decreases with the increase of CSS substitution.

Property comparison of steel slag cement mortar with hydroxyethyl methyl cellulose having different degrees of substitution and PAAm modification

The aim of this study is to explore the influence of HEMC with different total substitution degrees and polyacrylamide (PAAm) modification on the properties of steel slag cement mortar. The results show that HEMC increases the water retention rate, consistency, tensile bond strength, and flexibility of all types of steel slag cement mortars. The addition of HEMC, however, leads to a decrease in compressive strength and flexural strength. The total substitution degree or PAAm modification of HEMC has a minor effect on the water retention rate, compressive strength, flexibility, and pore size distribution of steel slag cement mortar. HEMC with a higher total substitution degree is more beneficial to the development of tensile bond strength except for SL1 cement mortar at an early age (3 days and 7 days), whereas PAAm weakens the positive effect of HEMC on the tensile bond strength. Mercury intrusion porosimeter (MIP) tests show that the addition of HEMC increases the porosity of steel slag cement mortar.