Sustainable quaternary binders made from metallurgical wastes of northeast Mexico: strength, hydration products, and durability.

In this research, four industrial wastes were used for up to 80% as supplementary cementitious materials (SCMs) in cement mortar systems: ground granulated blast furnace slag, electric arc furnace slag, basic oxygen furnace slag, and waste limestone powder. Quaternary cementitious blends were prepared and studied for up to 120 days. Workability, compressive strength, durability, microstructures, and sustainability studies were performed and compared with Portland cement references. Results showed that more than 30 MPa in compressive strength can be achieved by > 50% replacement with SCMs; only 9% below the reference. Neither H2SO4 nor MgSO4 attacks resulted in critical damages; nevertheless, curing under NaCl solution showed detrimental behavior. C-S-H with a low Ca/Si ratio was identified in the mortars as the main hydration product, possibly intermixed with stratlingite, C-A-S-H and/or hydrotalcite. Environmental impact for the blended cements was determined as the CO2eq. factor from a simple life cycle assessment. The embodied greenhouse gasses varied in 260.2-541.4 kg CO2eq./ton of binder depending on the formulation. This was 40-70% less than Portland cement (922.6 kg CO2eq./ton). The production of the raw materials dominated the polluting emissions, while freight, grinding, and sieving had little environmental impact.

An improvement in the method of correcting indirect radial strain measurements during triaxial strength tests in rocks.

The present article provides an improvement in the method to correct indirect strain measurements in triaxial compressive strength tests through axial displacement and hydraulic fluid volume change measurements. The improvement focused on reducing the parameters of the formula proposed for indirect volumetric strain in the original method, thereby facilitating the development of a simpler formula in which the radial strain depends on only two parameters: the initial volume of the rock specimen and the volume changes of the hydraulic fluid for each instant. The comparison between the improvement proposed, and original method resulted in a mean absolute difference of 0.003.•This improvement does not depend on the axial strain, unlike the original method, which requires correcting the indirect axial strain measurements before correcting the indirect radial strain measurements.•This improvement can be useful for research on the stress-strain behavior of intact rock under laboratory conditions, such as in the study of the post-peak state.

Study of Ultra-High Performance Concrete Mechanical Behavior under High Temperatures.

The main concern with concrete at high temperatures is loss of strength and explosive spalling, which are more pronounced in high-strength concretes, such as Ultra-High Performance Concrete (UHPC). The use of polymeric fibers in the mixture helps control chipping, increasing porosity and reducing internal water vapor pressure, but their addition can impact its mechanical properties and workability. This study evaluated the physical and mechanical properties of UHPC with metallic and PVA fibers under high temperatures using a 23 central composite factorial design. The consistency of fresh UHPC and the compressive strength and elasticity modulus of hardened UHPC were measured. Above 300 °C, both compressive strength and elasticity modulus decreased drastically. Although the addition of PVA fibers reduced fluidity, it decreased the loss of compressive strength after exposure to high temperatures. The response surface indicates that the ideal mixture-1.65% steel fiber and 0.50% PVA fiber-achieved the highest compressive strength, both at room temperature and at high temperatures. However, PVA fibers did not protect UHPC against explosive spalling at the levels used in this research.

Effects of Dolomitic Limestone on the Properties of Magnesium Oxysulfate Cement.

This study investigated the effects of substituting magnesium oxide (MgO) with dolomitic limestone (DL) on the mechanical and physical properties of magnesium oxysulfate (MOS) cement. Additionally, the hydration formation phases and the influence of the molar ratio on the MOS cement's performance were examined. The corresponding action mechanisms were identified and explored by compressive strength tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), isothermal calorimetry, and a thermogravimetric analysis (TGA). The results showed that replacing MgO with DL decreased the reaction speed and heat release rate generated in the hydration process of the MOS cement. This substitution also reduced the quantity of non-hydrated MgO particles and delayed the formation of Mg(OH)2. The diminished formation of Mg(OH)2 contributed to an increase in the apparent porosity of pastes containing DL, thus alleviating internal stresses induced by Mg(OH)2 formation and enhancing their mechanical strength after 28 days of curing. Conversely, the increased porosity improved the CO2 diffusion within the structure, promoting the formation of magnesium carbonates (MgCO3). Through the characterization of the cement matrix (XRD and TGA), it was possible to identify phases, such as the brucite, periclase, and 318 phases. The obtained results revealed the potential of incorporating mineral fillers like limestone as a promising approach to producing MOS cement with a reduced environmental impact and better properties at higher curing ages.

Sustainable Hybrid Lightweight Aggregate Concrete Using Recycled Expanded Polystyrene.

Global concrete production, reaching 14×1013m3/year, raises environmental concerns due to the resource-intensive nature of ordinary Portland cement (OPC) manufacturing. Simultaneously, 32.7×109 kg/year of expanded polystyrene (EPS) waste poses ecological threats. This research explores the mechanical behavior of lightweight concrete (LWAC) using recycled EPS manufactured with a hybrid cement mixture (OPC and alkali-activated cement). These types of cement have been shown to improve the compressive strength of concrete, while recycled EPS significantly decreases concrete density. However, the impact of these two materials on the LWAC mechanical behavior is unclear. LWAC comprises 35% lightweight aggregates (LWA)-a combination of EPS and expanded clays (EC) - and 65% normal-weight aggregates. As a cementitious matrix, this LWAC employs 30% OPC and 70% alkaline-activated cement (AAC) based on fly ash (FA) and lime. Compressive strength tests after 28 curing days show a remarkable 48.8% improvement, surpassing the ACI 213R-03 standard requirement, which would allow this sustainable hybrid lightweight aggregate concrete to be used as structural lightweight concrete. Also obtained was a 21.5% reduction in density; this implies potential cost savings through downsizing structural elements and enhancing thermal and acoustic insulation. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy reveal the presence of C-S-H, C-(A)-S-H, and N-A-S-H gels. However, anhydrous products in the hybrid LWAC suggest a slower reaction rate. Further investigation into activator solution dosage and curing temperature is recommended for improved mechanical performance on the 28th day of curing. This research highlights the potential for sustainable construction incorporating waste and underscores the importance of refining activation parameters for optimal performance.

ConcreteXAI: A multivariate dataset for concrete strength prediction via deep-learning-based methods.

Concrete is a prominent construction material globally, owing to its reputed attributes such as robustness, endurance, optimal functionality, and adaptability. Formulating concrete mixtures poses a formidable challenge, mainly when introducing novel materials and additives and evaluating diverse design resistances. Recent methodologies for projecting concrete performance in fundamental aspects, including compressive strength, flexural strength, tensile strength, and durability (encompassing homogeneity, porosity, and internal structure), exist. However, actual approaches need more diversity in the materials and properties considered in their analyses. This dataset outlines the outcomes of an extensive 10-year laboratory investigation into concrete materials involving mechanical tests and non-destructive assessments within a comprehensive dataset denoted as ConcreteXAI. This dataset encompasses evaluations of mechanical performances and non-destructive tests. ConcreteXAI integrates a spectrum of analyzed mixtures comprising twelve distinct concrete formulations incorporating diverse additives and aggregate types. The dataset encompasses 18,480 data points, establishing itself as a cutting-edge resource for concrete analysis. ConcreteXAI acknowledges the influence of artificial intelligence techniques in various science fields. Emphatically, deep learning emerges as a precise methodology for analyzing and constructing predictive models. ConcreteXAI is designed to seamlessly integrate with deep learning models, enabling direct application of these models to predict or estimate desired attributes. Consequently, this dataset offers a resourceful avenue for researchers to develop high-quality prediction models for both mechanical and non-destructive tests on concrete elements, employing advanced deep learning techniques.

Environmentally friendly concrete block production: valorization of civil construction and chemical industry waste.

In the present work, a study was carried out on the dosage of wastes from the chemical industry (tannery sludge) and civil construction (concrete and plaster) in mixtures used in concrete blocks' production. The objective was the application of these blocks in paving. The characterization of the materials used was performed employing X-ray diffractometry (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The effect of the different residues on the blocks' properties was evaluated through compressive strength, flexion-traction, water absorption, abrasion resistance, and leaching tests. The results indicated that the concrete paving blocks produced with the addition of residues did not obtain gains in the values of mechanical resistance to compression and traction in bending compared to blocks made with standard raw material. However, the blocks produced with construction waste presented satisfactory results for application in street paving after 7 days of concrete curing, reaching values between 36.54 and 44.6 MPa for the mentioned properties. These values also increased to 21.4% within 28 days of curing. The blocks produced with plaster showed values between 37.03 and 39.85 MPa after 28 days of curing, allowing their use for street paving. On the other hand, the blocks containing residues from the chemical industry had lower strengths, reaching a maximum of 29.36 MPa after 28 days of curing. In addition, it was also noted that the blocks produced with recycled concrete showed an improvement in performance for a composition of 50% recycled material.

Evaluation of Compressive and Bending Strength of a Geopolymer Based on Lateritic Clays as an Alternative Hydraulic Binder.

In Bolivia, lateritic soils are common in humid tropical regions and can be used in the construction industry as an alternative to materials that cause a negative environmental impact, such as cement. The production of Portland cement causes environmental issues like significant greenhouse gas emissions and air pollution. To address this problem, geopolymers have been introduced as an alternative binder with low CO2 emissions. In this regard, geopolymers based on lateritic clays have been studied mineralogically, chemically, and on their compressive strength separately. However, there are still no studies on lateritic clays present in Bolivia and their mechanical, mineralogical, and chemical properties combined in a geopolymer. Therefore, this present research proposes the evaluation of a geopolymer made from laterite clays. Compression and flexural tests were carried out, along with mineralogical and chemical analyses on mortar and geopolymer cubes and prisms. The results indicate that the laterite clay-based geopolymer has lower compressive strength compared to Portland cement IP (cement type I with the addition of pozzolana) mortar. However, the flexural strength tests show a slight increase in the case of the geopolymer.

Glass ionomer cement with calcium-releasing particles: Effect on dentin mineral content and mechanical properties.

OBJECTIVE: to evaluate the effect a glass ionomer cement (GIC) containing hydroxyapatite (HAp) or calcium silicate (CaSi) particles on mineral content and mechanical properties of demineralized dentin. Ion release and compressive strength (CS) of the cements were also evaluated. METHODS: GIC (Fuji 9 Gold Label, GC), GIC+ 5%HAp and GIC+ 5%CaSi (by mass) were evaluated. Ion release was determined by induced coupled plasma optical emission spectroscopy (Ca2+/Sr2+) or ion-specific electrode (F-) (n = 3). A composite (Filtek Z250, 3 M ESPE) was used as control in remineralization tests. Demineralized dentin discs were kept in contact with materials in simulated body fluid (SBF) at 37 °C for eight weeks. Mineral:matrix ratio (MMR) was determined by ATR-FTIR spectroscopy (n = 5). Dentin hardness (H) and elastic modulus (E) were determined by nanoindentation (n = 10). CS was tested after 24 h and 7d in deionized water (n = 12). Data were analyzed by ANOVA/Tukey test (α = 0.05). RESULTS: Ca2+ and Sr2+ release was higher for the modified materials (p < 0.05). Only GIC+ 5%HAp showed higher F- release than the control (p < 0.05). All groups showed statistically significant increases in MMR, with no differences among them after 8 weeks (p > 0.05). No differences in dentin H or E were observed among groups (p > 0.05). HAp-modified GIC showed increased initial CS, while adding CaSi had the opposite effect (p < 0.05). After 7 days, GIC+ 5%CaSi presented lower CS in relation to control and GIC+ 5%HAp (p < 0.05). SIGNIFICANCE: GIC modification with HAp or CaSi affected CS and increased ion release; however, none of the groups showed evidence of dentin remineralization in comparison to the negative control.

Influence of the ANN Hyperparameters on the Forecast Accuracy of RAC's Compressive Strength.

The artificial neural networks (ANNs)-based model has been used to predict the compressive strength of concrete, assisting in creating recycled aggregate concrete mixtures and reducing the environmental impact of the construction industry. Thus, the present study examines the effects of the training algorithm, topology, and activation function on the predictive accuracy of ANN when determining the compressive strength of recycled aggregate concrete. An experimental database of compressive strength with 721 samples was defined considering the literature. The database was used to train, validate, and test the ANN-based models. Altogether, 240 ANNs were trained, defined by combining three training algorithms, two activation functions, and topologies with a hidden layer containing 1-40 neurons. The ANN with a single hidden layer including 28 neurons, trained with the Levenberg-Marquardt algorithm and the hyperbolic tangent function, achieved the best level of accuracy, with a coefficient of determination equal to 0.909 and a mean absolute percentage error equal to 6.81%. Furthermore, the results show that it is crucial to avoid the use of overly complex models. Excessive neurons can lead to exceptional performance during training but poor predictive ability during testing.

Study of the Pozzolanic Reactivity of Sugar Cane Straw Ashes (SCSA) Burned under Controlled Conditions.

The aims of this work were to evaluate the reactivity of sugarcane straw ashes (SCSA) burned under controlled conditions and to analyze their reactivity in blended cement and hydrated lime pastes by thermogravimetric analysis (TG) and calorimetry. Four different ashes were produced, and burned at 600 °C, 700 °C, 800 °C and 900 °C (SCSA600, SCSA700, SCSA800 and SCSA900, respectively). These ashes were characterized by X-ray fluorescence spectroscopy, X-ray diffractometry, particle size distribution by laser diffraction and specific area surfaces to assess their potential interest in the partial replacement of inorganic binders (Portland cement (OPC) and hydrated lime). The hydrated lime pastes were subjected to scanning electron microscopy (SEM) and TG. The blended cement pastes were analyzed by TG and calorimetry, compressive strength testing and mercury intrusion porosimetry. High lime fixation percentages were observed in the hydrated lime and OPC pastes and were higher than 75% and 50% for the ashes burned at 600 °C and 700 °C, respectively. Calorimetry showed a delay in the heat release of SCSA600 and SCSA700 compared to the control paste. These pastes also had higher compressive strength and a smaller total pore volume. The results indicate the positive response of preparing sugar cane ashes under controlled conditions (mainly for straw calcined within the 600-700 °C range) for their use as pozzolanic addition by partially replacing inorganic binders.

Exploring the Potential of Alternative Materials in Concrete Mixtures: Effect of Copper Slag on Mechanical Properties and Carbonation Resistance.

In this study, the effect on the flowability, compressive strength, absorption, sorptivity, and carbonation resistance of concrete with different copper slag (CS) replacement ratios was investigated. For this research, four concrete mixes with different percentages of CS were made (0%, 10%, 20%, and 30% of CS as replacement of cement by volume). In addition, the microstructure was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TG-DTG). The results shows that the incorporation of CS reduces the workability and compressive strength of the mixtures, being more significant in concrete with 30% CS. The carbonation depth of concrete with CS increases monotonically with increasing CS. In addition, the compressive strength of the carbonated (20% and 30% CS) concretes show a loss of compressive strength at 90 days of exposure when compared to their water-cured counterparts. The use of low percentages of CS does not generate a decrease in workability and its mechanical effect is not significant at prolonged ages, so the use of this waste as SCM in percentages close to 10% is a viable alternative to the sustainability of concrete and the management of this residue.

Análisis In vitro de yesos dentales de alta resistencia y baja expansión disponibles en Perú / In vitro analysis of high resistance and low expansion dental plasters available in Peru

Objetivo. Comparar la dureza, estabilidad dimensional y resistencia a la compresión de los yesos dentales de alta resistencia y baja expansión disponibles en el Perú. Métodos. Se realizó un estudio descriptivo, observacional y transversal. Se confeccionaron muestras de forma cilíndrica (8) y rectangular (8), de siete yesos dentales de alta resistencia y baja expansión. Se evaluó la dureza utilizando el Durómetro Universal Identec, la estabilidad dimensional con un calibrador digital y la resistencia a compresión con la Máquina de Ensayo Universal. Para determinar si hay diferencia en cada una de estas propiedades se empleó el análisis de varianza, la prueba F y la prueba de Duncan. Además, se empleó la prueba de comparación de medias, t de Student, para evaluar si difieren con los valores de la ADA (Asociación Dental Americana). Resultados. La dureza, estabilidad dimen-sional y resistencia a la compresión promedio de los yesos dentales presentó diferencias significativas (p<0.05) entre cada uno con los promedios estándares establecidos por la ADA. Conclusiones. En relación resistencia a la compresión el 100% de los yesos analizados cumplen con los parámetros establecidos por la ADA, en relación estabilidad dimensional solo el 28.6% y el 100% no alcanzan los estándares de dureza promedio establecidos por la ADA.

Objective. To compare the hardness, dimensional stability, and compressive strength of high-strength, low-expansion dental plasters available in Peru, according to ADA criteria. Methods. A descriptive, observational and cross-sectional study was developed. A selection of 8 cylindrical-shaped samples and 8 rectangular- shaped ones, from seven high-resistance, low-expansion dental plasters were fabricated. The hardness was evaluated using the Identec Universal Durometer. Dimensional stability was evaluated with a digital caliper and compressive strength was evaluated with the Instron Universal Testing Machine. To determine if there is a difference in each of these properties, the analysis of variance, F test, and the Duncan's test were used. In addition, to assess whether these values differ from those of the ADA, the mean comparison test, student's t table, were used. Results. The hardness, dimensional stability and average compressive strength of the high-strength, low-expansion dental plasters showed that there are significant di-fferences (p<0.05) between each of the dental plasters and with the standard averages established by the American Dental Association. (ADA). Conclusions. 100% of the high-strength, low-expansion dental casts meet the parameters established by the ADA in terms of their compressive strength, only 28.6% of these comply with the ADA in terms of dimensional stability and that 100% of these do not meet the average hardness standards established by the ADA.

Influence of alveolar bone height on the biomechanical behavior of roots restored with custom-made posts-and-cores.

OBJETIVE: This study evaluated the influence of alveolar bone height and post type on compressive force resistance, fracture pattern, and stress distribution in endodontically treated teeth. MATERIALS AND METHODS: Bovine roots were endodontically treated and divided into eight groups (n = 10) according to alveolar bone height (normal alveolar bone and alveolar bone loss - 2 and 5 mm from the margin of the crown, respectively) and post type (prefabricated glass fiber post, anatomic glass fiber post, customized milled glass fiber post-and-core and customized milled polyetheretherketone (PEEK) post-and-core). Mechanical fatigue was simulated (300.000 cycles/50 N/1.2 Hz). Compression force resistance (N) was analyzed by two-way ANOVA and Tukey test (α = 0.05). Fracture patterns were described as percentages. Stress distribution was analyzed by finite element analysis. RESULTS: Significant diferences were found for alveolar bone height (P < 0.0001): normal alveolar bone groups showed higher mean values of compression force resistance compared to alveolar bone loss groups, while no significant differences were found for post type (P = 0.4551), and there was no double interaction between them (P = 0.5837). Reparable fractures were more predominant in normal alveolar bone groups, especially in the milled glass fiber and PEEK post-and-core groups. Stress distribution was similar in groups with prefabricated glass fiber posts and milled PEEK posts-and-cores, and the alveolar bone loss condition significantly increased stress concentration and strain values, mainly on apical dentin. CONCLUSIONS: Alveolar bone loss due to physiological aging and/or periodontal disease may lead to increased risk of restored tooth failure, although milled glass fiber and PEEK posts-and-cores provide more reparable fractures. CLINICAL SIGNIFICANCE: Custom-made glass fiber and PEEK post-and-cores are interesting options, since they enable clinicians to work with a single-body post-and-core system that avoid several materials interfaces and fits well in the root canal provided promising results to improve the failure behavior of restored roots, as they offer more reparable fractures even in situations of alveolar bone loss.

Development of a Portland Cement-Based Material with Agave salmiana Leaves Bioaggregate.

Depending on the morphology of the natural fibers, they can be used as reinforcement to improve flexural strength in cement-based composites or as aggregates to improve thermal conductivity properties. In this last aspect, hemp, coconut, flax, sunflower, and corn fibers have been used extensively, and further study is expected into different bioaggregates that allow diversifying of the raw materials. The objective of the research was to develop plant-based concretes with a matrix based on Portland cement and an aggregate of Agave salmiana (AS) leaves, obtained from the residues of the tequila industry that have no current purpose, as a total replacement for the calcareous aggregates commonly used in the manufacturing of mortars and whose extraction is associated with high levels of pollution, to improve their thermal properties and reduce the energy demand for air conditioning in homes. Characterization tests were carried out on the raw materials and the vegetal aggregate was processed to improve its compatibility with the cement paste through four different treatments: (a) freezing (T/C), (b) hornification (T/H), (c) sodium hydroxide (T/NaOH), and (d) solid paraffin (T/P). The effect of the treatments on the physical properties of the resulting composite was evaluated by studying the vegetal concrete under thermal conductivity, bulk density, and compressive strength tests with a volumetric ratio between the vegetal aggregate and the cement paste of 0.36 and a water/cement ratio of 0.35. The hornification treatment showed a 15.2% decrease in the water absorption capacity of the aggregate, resulting in a composite with a thermal conductivity of 0.49 W/mK and a compressive strength of 8.66 MPa, which allows its utilization as a construction material to produce prefabricated blocks.

Evaluation of CNTs and SiC Whiskers Effect on the Rheology and Mechanical Performance of Metakaolin-Based Geopolymers.

Despite geopolymers having emerged as a more sustainable alternative to Portland cement, their rheological properties still need to be thoroughly investigated, aiming at the material's applicability. Additionally, studies that evaluated the fresh state of geopolymer composites with nanomaterials are scarce. Thus, two metakaolin-based geopolymer systems were reinforced with nanomaterials with a similar geometry: carbon nanotubes (CNT) and silicon carbide whiskers (SCW). The nanomaterials incorporation was assessed by rotational rheometry (conducted up to 110 min), isothermal calorimetry, compressive strength after 7 and 28 days, and the microstructure was investigated using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). CNT and SCW incorporation (0.20 wt.%) did not significantly affect the yield stress and viscosity of the R2-group (based on metakaolin type 2), while increasing the rheological parameters up to 56.0% for the R1-group (based on metakaolin type 1). Both additions modified the reaction kinetics. Increments of up to 40.7% were observed in the compressive strength of geopolymer pastes with the incorporation of a SCW content of 0.2 wt.%. XRD and FTIR results suggest similar structural modifications between precursors. Nevertheless, R2 showed substantial transformations while the R1 group exhibited anhydrous material that can react over time. Overall, incorporating CNT and SCW contributed to higher mechanical increments on systems with average mechanical strength (R1) compared to systems with higher potential mechanical performance (R2).

Mechanical Properties and Antibacterial Effect on Mono-Strain of Streptococcus mutans of Orthodontic Cements Reinforced with Chlorhexidine-Modified Nanotubes.

Recently, several studies have introduced nanotechnology into the area of dental materials with the aim of improving their properties. The objective of this study is to determine the antibacterial and mechanical properties of type I glass ionomers reinforced with halloysite nanotubes modified with 2% chlorhexidine at concentrations of 5% and 10% relative to the total weight of the powder used to construct each sample. Regarding antibacterial effect, 200 samples were established and distributed into four experimental groups and six control groups (4 +ve and 2 -ve), with 20 samples each. The mechanical properties were evaluated in 270 samples, assessing microhardness (30 samples), compressive strength (120 samples), and setting time (120 samples). The groups were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy, and the antibacterial activity of the ionomers was evaluated on Streptococcus mutans for 24 h. The control and positive control groups showed no antibacterial effect, while the experimental group with 5% concentration showed a zone of growth inhibition between 11.35 mm and 11.45 mm, and the group with 10% concentration showed a zone of growth inhibition between 12.50 mm and 13.20 mm. Statistical differences were observed between the experimental groups with 5% and 10% nanotubes. Regarding the mechanical properties, microhardness, and setting time, no statistical difference was found when compared with control groups, while compressive strength showed higher significant values, with ionomers modified with 10% concentration of nanotubes resulting in better compressive strength values. The incorporation of nanotubes at concentrations of 5% and 10% effectively inhibited the presence of S. mutans, particularly when the dose-response relationship was taken into account, with the advantage of maintaining and improving their mechanical properties.

Compressive Strength Assessment of Soil-Cement Blocks Incorporated with Waste Tire Steel Fiber.

The rapid growth in waste tire disposal has become a severe environmental concern in recent decades. Recycling rubber and steel fibers from wasted tires as construction materials helps counteract this imminent environmental crisis, mainly improving the performance of cement-based materials. Consequently, the present article aims to evaluate the potential use of waste tire steel fibers (i.e., WTSF) incorporated in the manufacture of soil-cement blocks, considering their compressive resistance as a primary output variable of comparison. The experimental methodology applied in this study comprised the elaboration of threefold mixtures of soil-cement blocks, all of them with 10% by weight in Portland cement, but with different volumetric additions of WTSF (i.e., 0%, 0.75%, and 1.5%). The assessment's outcomes revealed that the addition of 0.75% WTSF does not have a statistically significant influence on the compressive resistance of the samples. On the contrary, specimens with 1.5% WTSF displayed a 20% increase (on average) in their compressive strength. All the tested samples' results exhibited good agreement with the minimum requirements of the different standards considered. The compressive resistance was evaluated in the first place because it is the primary provision demanded by the specifications for applying soil-cement materials in building constructions. However, further research on the physical and mechanical properties of WTSF soil-cement blocks is compulsory; an assessment of the durability of soil-cement blocks with WTSF should also be carried out.

Hybrid Cements with ZnO Additions: Hydration, Compressive Strength and Microstructure.

The effect of ZnO has already been studied for Portland cement, but the study of its impact on hybrid pastes is scarce. Thus, in this investigation, the influence of ZnO addition on hydration, compressive strength, microstructure, and structure of hybrid pastes is presented. The analyses were made by setting time tests, compressive strength tests, X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis with differential scanning calorimetry, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The results indicate that the setting time of the cements was delayed up to 39 min with additions of 3 wt% ZnO. Alternatively, the higher values of compressive strength were observed when 0.5 wt% ZnO was added to the cements for all curing days. In addition, no important differences in the microstructure of samples with different additions of ZnO were observed after 28 days of curing. It is expected that the use of ZnO contributes to the delay of the setting time and the increase of the compressive strength without negatively modifying the microstructure of hybrid pastes.

Fracture strength of extended class I composite restorations with different restorative techniques.

To evaluate the fracture strength of extended Class I restorations with different restorative techniques using nanofilled and nanohybrid composites. Sixty extracted human third molars were prepared with extended Class I cavities and divided into six groups: groups FS-F (Filtek bulk-fill Flow + Filtek Supreme Ultra, 3 M) and GR-F (X-tra base + GrandioSO, VOCO), restored with a flowable bulk-fill composite as a base covered by a nanofilled or nanohybrid composite; groups FB (Filtek One Bulk-Fill, 3 M) and AF (Admira Fusion X-tra, VOCO), restored with a bulk-fill resin composite; and groups FS (Filtek Supreme Ultra, 3 M) and GR (GrandioSO, VOCO), restored incrementally with a nanofilled or nanohybrid composite. Sound extracted teeth (n = 10) were used as a control group (CTL). The specimens were axially loaded until failure. Data were analyzed using one-way ANOVA and Games Howell test (α = 0.05). Groups CTL and GR-F demonstrated significantly higher mean fracture strength when compared to FS, AF, and GR (p < 0.05). Group AF obtained more repairable fractures than the other groups. Restorations made with a nanofilled bulk-fill composite or with conventional resin composites associated with a flowable bulk-fill base were able to reestablish the fracture strength to that of sound teeth.