Influence of PZT volume fraction, composite thickness and cement matrix on the performance of d15 shear mode 1–3 connectivity cement-based piezoelectric composites

The aim of this study was to evaluate and to compare clinical and radiographic outcomes of 4 materials (formocresol, mineral trioxide aggregate (MTA), Portland cement and enamel matrix derivative) using in primary teeth pulpotomies. Sixty-five patients aged 5-9 years (32 female, 33 male) were included in this study. A total of 140 primary first and second molars with deep caries were treated with pulpotomy. All teeth were then restored with stainless steel crowns. The treated teeth were evaluated clinically and radiographically at 3, 6, 12, 18 and 24 months. At 24 months, the clinical success rates of formocresol, MTA, Portland cement, and enamel matrix derivative were 96.9%, 100%, 93.9%, and 93.3%, respectively. The corresponding radiographic success rates were 84.4%, 93.9%, 86.7% and 78.1%, respectively. Although there were no statistically significant differences in clinical and radiographic success rates among the 4 groups, MTA appears to be superior to formocresol, Portland cement, and enamel matrix derivative as a pulpotomy agent in primary teeth.

Reinforcement effects of polyvinyl alcohol and polypropylene fibers on flexural behaviors of sulfoaluminate cement matrices

Circular alternatives in the construction industry: An environmental performance assessment of sisal fiber-reinforced composites

Effect of matrix modification on the durability of cementitious composites reinforced with aligned Ensete fibre

Novel three-phase piezoelectric composites that comprised lead zirconate titanate (PZT), aluminium and Portland cement were fabricated at a low poling voltage of 0·6 kV/mm and temperature of 160°C. Aluminium and PZT particles were distributed in a Portland cement matrix, and the dielectric constant, tan δ and strain coefficients were experimentally investigated as a function of inclusion volume fraction. The three-phase piezoelectric composites were found to possess higher piezoelectric strain coefficients, d33, than their two-phase counterparts (PZT and Portland cement composites). The highest value of d33observed for the three-phase composite was 8·1 pC/N for volume fractions of 0·7 and 0·2 for PZT and aluminium respectively, which was 164% of the value observed for the two-phase composite, at the same PZT volume fraction. An analytical model was used to predict values for the effective dielectric constant of the three-phase composites, and these values compared reasonably well to the empirical data. An investigation of sample degradation as a function of time was performed. Samples showed the highest degree of reduced dielectric performance occurred within two days of data capture, and minimal subsequent reduction in performance after 300 d. Electrical properties of the composites are influenced by the oxidation of aluminium by the alkaline constituents in the cement matrix, distribution of PZT and aluminium within the matrix, particle agglomeration, inclusion size, contact resistance between particles and air voids. The increased dielectric and piezoelectric strain coefficients, demonstrate that these types of materials may be useful in applications such as structural health monitoring and energy harvesting.

The high consume of crustaceans in human food has generated a large quantities of residues, such as the crab shell of Ucides cordatus (caranguejo-uçá), in Brazil. These residues are disposed in the environment. The development of new materials using crab shells chitin for biotechnological applications in civil construction is of great interest to the scientific community. The residues addition in the cement can reduce electricity consumption, CO2 emissions and other environmental damage from this human activity. Thus, the aims of this study were the use of U. Cordatus residues for hydroxyapatite and chitosan production and the incorporation of these compounds in Portland cement matrix, as a viable alternative to improve the properties of the paste and mortar when fresh or hardened. The crab shells were obtained from a fishermen's cooperative after meat extraction. The cement for the production of pastes and mortars was CPII F-40 Portland with filer. The proportion of biomaterial in the cement matrix was of 1 to 5% (w/w). The physical and chemical properties of this material were determined in the fresh and hardened states. Biopolimers of the crab shells promoted changes in consistency, reduced setting time of pastes and mortars and an increase in strength to the axial compressive. These changes may be due to the hydrophilic groups of this compound and the greatest water retention that causes increase the number of nucleation points of the cement and paste grains becomes denser and homogeneous. Thus, the addition of biopolimers in the cement matrix may function as a polyfunctional additive. Furthermore, this process contributes to the reduction of environmental damage caused by improper disposal of crab shells and may represent an economic enhancement of this by-product of the food industry.

Micromechanical properties of cement matrices in cementitious composites were investigated by means of the microindentation method. The research focused on the correlation between micromechanical properties such as modulus of elasticity and creep, and distance of the indentation from the aggregate-matrix interface. Composites based on ordinary Portland cement (OPC) matrix were examined after exposure to two types of ageing procedures. The sub-micron accuracy of the positioning system of the microindentation apparatus provided means for a meaningful investigation of cement matrix in close vicinity to the aggregate-matrix interface. For the purpose of statistical analyses, the data were divided into two groups with respect to the distance of the indent from the aggregatematrix interface. While the tests performed within a 30 μm distance from the interface were classified as indents within the interfacial transition zone (ITZ), indents outside this distance were considered to describe properties of the ‘bulk matrix’. The results provide quantitative comparison of the microstructural properties of the interfacial transition zone (ITZ) with those of the bulk cement matrix assessed by well understood characteristics such as elastic modulus and creep. It was shown that, for unaged specimens, the elastic modulus measured within the interfacial transition zone was about 25% lower than that of the bulk matrix. Such results have significant consequences for improvement in modelling of cementitious composites.

Reinforcement-matrix interactions and their consequences on the mechanical behavior of basalt fibers-cement composites

Solidification/stabilization of heavy metals in latex modified portland cement matrices

Based on a waste generated survey by companies in the area of the city of Bahia Blanca (Argentina), the possibility of incorporating part of them in a Portland cement matrix was examined. Among the waste is toner (TW), which is obtained from cartridges used in photocopiers, laser printers, and faxes. This paper aims to analyze the physical and mechanical properties of cement pastes and mortars using toner as a Portland cement replacement compared to a reference sample without toner. The mixes were made with 2.5, 5, 10, and 15 wt.% replacement of cement by toner, and it was measured the flow, normal consistency, setting time, calorimetry, and Frattini test in pastes and mechanical strengths in mortars employing standardized tests. Also, an analysis of the leachate in the curing water was carried out after 56 days to look for contaminating materials. The replacement of up to 5% cement with toner did not produce substantial alterations in the final setting time or mechanical properties. No heavy metals were found in the leachate, so TW can be immobilized in a cementitious matrix as it does not cause leaching above the established limits. Therefore, TW from a local industry can be used in construction materials and could contribute to a reduction of up to 14% of CO2 emissions with a cement replacement of 15% in cement-based materials.

Penetration and diffusion of chloride ions in concrete can lead to the corrosion of steel bar and shorten the service life of concrete structures. Phosphoaluminate cement (PAC) is a new cementitious material which has many special properties compared to Portland cement (PC). In the study, chloride ion diffusion in PAC concrete was tested with RCM method. The phase composition and morphology of hydration products, pore volume of hardened paste cured for 28d were analyzed with X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP). The results show that chloride ion diffusion coefficient of PAC concrete is much lower than that of Portland cement concrete under the same test conditions. The hydration products of PAC are main micro-crystalline phase and gel of phosphate and/or phophoaluminate, which formed a dense microstructure. There is no calcium hydroxide produced in the PAC hydration system. In hardened PAC paste, chloride ions might replace the atom group [OH] - and [PO4]3- of hydrates and become stable compounds. The resistance to chloride ion diffusion of PAC concrete will increase with the hydration age, because its microstructure becomes denser with the hydration age increasing.

A comparative study of the fracture features, strength and deformation properties of pseudo strain-hardening composites based on alkali-activated slag and Portland cement matrices with polypropylene microfiber was carried out. Correlations between their compositions and characteristics of stress–strain diagrams under tension in bending with an additional determination of acoustic emission parameters were determined. An average strength alkali-activated slag matrix with compressive strength of 40 MPa and a high-strength Portland cement matrix with compressive strength of 70 MPa were used. The matrix compositions were selected for high filling the composites with polypropylene microfiber in the amount of 5%-vol. and 3.5%-vol. ensuring the workability at the low water-to-binder ratios of 0.22 and 0.3 for Portland cement and alkali-activated slag matrices, respectively. Deformation diagrams were obtained for all studied compositions. Peaks in the number of acoustic signals in alkali-activated slag composites were observed only in the strain-softening zone. Graphs of dependence of the rate of acoustic events occurrence in samples from the start of the test experimentally prove that this method of non-destructive testing can be used to monitor structures based on strain-hardening composites.

Modification of Portland cement matrix with diethyldithiocarbamate for technetium immobilization

Improvement of the durability of glass fiber reinforced cement using blended cement matrix

It is often of great importance in engineering to know precisely the properties of a material used with regard to its strength, its plasticity or its brittleness, its elasticity, and some other properties. For this purpose, material samples are tested in a tensile test by clamping the sample with a known starting cross-section in a tensile testing machine and loading it with a tensile force F. The force is then graphically displayed over the length change ΔL caused. This curve is called the force-extension diagram. In this study, a new measurement method enables for the first time, depending on the applied uniaxial stress, an insight at the atomic level into various energy dissipation processes at cement-based materials with the help of infrared spectroscopy. The samples are modified by adding SiO2 particles, which are coated by a polymer (PEG-MDI-DMPA) of different PEG molecular weights. Results show that elongating and breakage of [Formula: see text] and [Formula: see text] bonds play an essential role in the strain energy dissipation. Compared to the pure cement, the modified samples are affected more by elongating and breakage of [Formula: see text] as the admixture can effectively reduce the energy barrier of the hydrolytic reaction. The incorporating of particles into the cement matrix induces new mechanisms for energy dissipation by stretching of [Formula: see text] bending vibrations. Stretching vibration of the [Formula: see text] group indicates that part of the energy is dissipated by breakage of hydrogen bonding between the carboxyl group and PEG chains. Besides, a higher value of the ultimate fracture force following an increase in the molecular weight of PEG shows stronger bonding between particles and the cement matrix. As the chain-length of PEG is increased, less energy is absorbed through the other processes (especially at a higher level of strain). Thus, there is a balance between the whole deformation (toughness) and the strength of samples with the increase of the PEG molecular weight.