Hybrid concretes: solutions for better bond and splitting tensile strength under elevated heat exposure

PurposeThis paper presents the second part of the investigation on resistance to elevated temperatures of a proposed hybrid composite concrete (NCSF-Crete) mix. The composite including nano metakaolin (NC) and steel fibers (SF) in addition to regular concrete components has proven -in the first published part-earlier promoted fresh concrete behavior, and to have reduced loss in compressive strength after exposure to a wide range of elevated temperatures. This presented work evaluates another two critical mechanical characteristics for the proposed composite -namely- splitting and bond strengths.Design/methodology/approachA modified formula correlating splitting and compressive strength (28 days) based on experiments results for NCSF is proposed and compared to formulas derived for regular concrete in different design codes. Finally, both spitting and bond strengths are evaluated pre- and post-exposure to elevated temperatures reaching 600 °C for two hours.FindingsThe proposed NCSF-Crete shows remarkable fire endurance, especially in promoting bond strength as after 600 °C heat exposure tests, it maintained strength equivalent to 70% of a regular concrete control mix at room temperature. Improving residual splitting strength was very significant up to 450 °C exposure.Research limitations/implicationsObvious deterioration is monitored in splitting resistance for all concretes at 600 °C.Practical implicationsThis proposed composite improved elevated heats resistance of the most significant concrete mechanical properties.Social implicationsUsing a more green and sustainable constituents in the composite.Originality/valueThe proposed composite gathers the merits of using NC and SF, each has been investigated separately as an addition to concrete mixes.

Tick Infestation and Piroplasm Infection in Barbarine and Queue Fine de l’Ouest Autochthonous Sheep Breeds in Tunisia, North Africa

As ticks and tick-borne pathogens affect the productivity of livestock, searching for genetically resistant breeds to infestation by ticks may represent an alternative to the overuse of chemical drugs. The aim of this study was to assess if there is a difference in tick infestation among the main sheep breeds in Tunisia. The study was carried out between April 2018 and January 2020 in 17 small to middle-sized sheep flocks from 3 regions across Tunisia. Four hundred and thirty-nine ear-tagged ewes from Barbarine (n = 288, 65.6%) and Queue Fine de l’Ouest (QFO) (n = 151, 34.4%) breeds were examined and sampled each trimester. Ticks were identified to the species level, and piroplasms were detected using PCR that targets a common sequence ARNr18S to both Babesia and Theileria genera using catch-all primers. Totally, 707 adult ticks were collected from animals; 91.4% (646/707) of them were Rhipicephalus sanguineus s.l. Queue Fine de l’Ouest animals were markedly less infested by ticks, and no one of them was infected by piroplasms compared to the Barbarine breed. Indeed, during the first four seasons, 21 animals, all from the Barbarine breed, were detected positive for piroplasms. This is the first study in Tunisia about the low susceptibility of QFO ewes to infestation by ticks and to infection by piroplasms. The QFO sheep breed could be raised preferably at high-risk areas of tick occurrence and could be considered in concrete control strategies, including a breeding program.

Effect of the Notch-to-Depth Ratio on the Post-Cracking Behavior of Steel-Fiber-Reinforced Concrete

Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically and experimentally the effect of the addition of the steel fibers on the performance of the post-cracking stage on fiber-reinforced concrete, by studying four notch-to-depth ratios of 0, 0.08, 0.16, and 0.33. This was evaluated through 72 bending tests, using plain concrete (control) and fiber-reinforced concrete with volume fibers of 0.25% and 0.50%. Results showed that the specimens with a notch-to-depth ratio up to 0.33 are capable of attaining a hardening behavior. The study concludes that the increase in the dosage leads to an improvement in the residual performance, even though an increase in the notch-to-depth ratio has also occurred.

Preliminary Studies of Ca-Al-Layered Double Hydroxide (Ldh) and Its Effect on the Compressive Strength in Concrete

This research work involved the preliminary studies of CaAl-LDHs using co precipitation method and applying it in the preparation of concrete to evaluate the compressive strength in grade 15 concrete. Slum and compressive strength test were carried out on the concrete control and concrete mixed with CaAl-LDH, Scanning electron microscope (SEM) and X-Ray Diffractogram (XRD) was carried out on the synthesize LDH, concrete control, and concrete mixed with LDH. From the results obtained in the work failure load test, it was observed that there was an increase by 62.60% in the compressive strength of concrete mixed with 30kg of CaAl-LDHs, the SEM micrograph also shows the increase in the density and the less porosity of the concrete mixed with CaAl-LDH which explained the increase in the compressive strength of the concrete. CaAl-LDH has therefore shows a promising effect on the increase on the compressive strength of concrete.

Influence of Partial Replacement of Cement and Sand with Coal Bottom Ash on Concrete Properties

An experimental study was accomplished to study the effect of replacement of both cement and sand with coal bottom ash (CBA) on the properties of the concrete. Control mix was prepared without coal bottom ash replacement and nominated as series A. The mixes of series B were prepared with20 % replacement of cement with 30 hours ground coal bottom ash (GCBA). Mixes of series C were prepared with four percentages (5,10,15,20) of CBA as partial replacement of sand. Mixes of Series D mixes were prepared as a combination of series B and C. Slump flow, compressive strength, and water permeability properties were investigated. Series D mixes showed lower workability compared to the series C mixes and control mix. Compressive strength of series D mix gained slightly higher strength compared to the control mix but lower than series C strength. Series C mixes absorbed more water compared to control mix concrete. Series D mixes achieved lower water permeability coefficient compare to series C which showed lower water permeability than the control.

O konstytucyjnym pojęciu godności osobowej

The content of this publication is a presentation of the meaning of the formula which refers to human dignity. The understanding of this idea should always remain in accordance with the legislative and judicial acquis of countries of western civilisation sphere. Based on judicature and source literature, respective attributes of human dignity, which Article 30 of the Constitution of the Republic of Poland refers to, have been explained. A change of the attitudes of constitutional lawyers’ community and the Constitutional Tribunal has been highlighted, with the possibility of referring to the content of this article as an independent model of constitutionality of law under an abstract and concrete control. Initially, human dignity was considered as a general rule and not legal rights.

MECHANICAL AND SHRINKAGE PROPERTIES OF HYBRID STEEL AND POLYPROPYLENE FIBRE REINFORCED CONCRETE COMPOSITE

An experimental study had been carried out to investigate the mechanical properties, expansion and shrinkage of fibre reinforced concrete composite (FRC). However, instead of using single type fibre of either steel (SF) or polypropylene (PPF), this study also combined the two types in one mix.The mechanical properties investigated in this study include compressive strength, splitting tensile strength and flexural strength. Three different FRC mix proportions and one normal concrete (control) were casted which includes (a) 75% SF, (b) 75% SF + 25% PPF, (c) 25% PPF, and (d) 0% fibre for control (PC). Meanwhile, the volume fraction, Vf for the FRC was fixed at 1.5% and the concrete strength was designed to achieve grade C60 at 28 days. The results show that the use of fibres in concrete decreased the workability of concrete. In addition, concrete mix with both SF and PPF produced the highest splitting tensile and flexural strengths by an increase of 75.9% and 86.5%, respectively as compared with the control. Furthermore, expansion and shrinkage of FRC was found to be less than the control. It can be concluded that the combined SF and PPF in concrete gives the most appropriate combination as regards to the highest flexural and splitting tensile strengths, and also reduced the shrinkage strain.

Comparison of the rate of claw horn growth and wear and sole thickness in dairy cattle housed in a free stall barn with concrete and rubber flooring

Background. Thin soles and resulting lameness in cows are often due to abrasive walking surfaces that cause increased wear. The aim of this project was to compare horn growth and wear and sole thickness in cows kept on rubber mats versus concrete in a free-stall barn. Methods. To examine horn growth and wear and sole thickness, we examined two groups (Group 1 kept on concrete [control] and Group 2 on rubber mats) of 12 cows each at 2-week intervals over a 12-week period. The 12 cows in each group were selected to achieve equal parity in each group, as follows: four cows, parity 1; four cows, parity 2; two cows, parity 3; and two cows, parity 4. The four cows from the parity 1 group had the most days in milk in the herd irrespective of milk production. The remaining eight cows had the fewest days in milk (most recently calved) irrespective of milk production. Results. Cows in the control group had a significant increase in claw horn growth over the study period, compared to the control group. Most of this difference in horn growth occurred during the first 2 weeks of the study. There was no significant difference in claw horn wear and sole thickness at 2 weeks or at the end of the study. There was, however, a non-significant difference in wear between cows in the 2 groups at the end of the study, with cows in the control group showing most wear. Cows in the experimental group exhibited significant increases in all parameters (claw length, wear, and growth; sole thickness) when measured at the beginning and end of the trial, whereas cows in the control group showed a significant increase in claw length and sole thickness.Discussion. These findings suggest that there was a compensatory increase in horn production in response to accelerated claw horn wear in the control group. Statistical significance in wear might have been attained between groups at the end of the study if the study had continued over a longer period.

Comparison of the rate of claw horn growth and wear and sole thickness in dairy cattle housed in a free stall barn with concrete and rubber flooring

Background. Thin soles and resulting lameness in cows are often due to abrasive walking surfaces that cause increased wear. The aim of this project was to compare horn growth and wear and sole thickness in cows kept on rubber mats versus concrete in a free-stall barn. Methods. To examine horn growth and wear and sole thickness, we examined two groups (Group 1 kept on concrete [control] and Group 2 on rubber mats) of 12 cows each at 2-week intervals over a 12-week period. The 12 cows in each group were selected to achieve equal parity in each group, as follows: four cows, parity 1; four cows, parity 2; two cows, parity 3; and two cows, parity 4. The four cows from the parity 1 group had the most days in milk in the herd irrespective of milk production. The remaining eight cows had the fewest days in milk (most recently calved) irrespective of milk production. Results. Cows in the control group had a significant increase in claw horn growth over the study period, compared to the control group. Most of this difference in horn growth occurred during the first 2 weeks of the study. There was no significant difference in claw horn wear and sole thickness at 2 weeks or at the end of the study. There was, however, a non-significant difference in wear between cows in the 2 groups at the end of the study, with cows in the control group showing most wear. Cows in the experimental group exhibited significant increases in all parameters (claw length, wear, and growth; sole thickness) when measured at the beginning and end of the trial, whereas cows in the control group showed a significant increase in claw length and sole thickness.Discussion. These findings suggest that there was a compensatory increase in horn production in response to accelerated claw horn wear in the control group. Statistical significance in wear might have been attained between groups at the end of the study if the study had continued over a longer period.