Minimum Strength Values Research Articles

The influence of methods of concrete quality control by physical and mechanical parameters on the reliability of building structures

Introduction. The construction technical control system evaluates the physical and mechanical properties of concrete on the base of testing a series of samples taken from a batch of concrete. It is necessary to take into account the influence of the control method on the quality of concrete structures and their reliability.
 
 Aim. Creation of a technical control system that should eliminate the causes of the identified risks by reducing the impact of the identified causes.
 
 Materials and methods. The control method affects the reliability of concrete structures being built and is evaluated from the point of view of choosing the number of samples and discarding the minimum strength values in the series. The results of the control of a series of concrete samples for 6 samples selected in such a way as to ensure compliance with the declared class when discarding 2 minimum sample values are compared.
 
 Results. As a result of the analysis of the impact of the methodology on quality and reliability: class B turns out to be 2 steps lower than the prescribed one, the in-series coefficient of variation exceeds the permissible one by 8 %, and the reliability level is significantly lower by 36 %.
 
 Conclusions. The conducted research shows an underestimation of the methodological component of material control, which can leave significant gaps in the system of technical control of construction products and does not allow to ensure the required level of reliability of structures.

Influence of welding thermal cycles on properties of TMCP and Q&T steels evaluated by thermo-physical simulation

The welding process represents an unintentional, but unavoidable, heat treatment in the form of soft annealing or tempering, but also hardening during the cooling of the melt. Particularly in the case of high-strength fine-grained structural steels, this leads to critical states of the mechanical-technological properties of the base material. In order to investigate the influence of the heat input during welding on the resulting properties of the heat-affected areas, a thermo-physical simulation was carried out on a quenching and forming dilatometer Bähr DIL 805 A/D, considering low-alloyed quenched and tempered (Q&T) and low-alloyed thermo-mechanically controlled processed steels (TMCP) with yield strengths in the range of 500 to 960 MPa (S500MC, S700MC, S770QL, and S960QL). For this purpose, time–temperature cycles based on gas metal arc welding (GMAW) were simulated with different maximum temperatures (1200 °C; 1000 °C; 800 °C), representing the typical microstructural regions of the heat-affected zones (HAZ), and cooling times t8/5 (5 s; 12 s; 20 s; 25 s) on miniature tensile specimens. To evaluate the property changes of the characteristic HAZ, tensile tests, hardness measurements, and microstructural investigations were analyzed. The investigations illustrate the significant influence of heat input during the welding process on the resulting mechanical-technological properties and microstructure for both kinds of steel. It was demonstrated that all the steels investigated tend to soften with increasing cooling times. The investigated Q&T steels have a lower risk of falling below the strength of the untreated base material than the investigated TMCP fine-grained structural steels. The considerably pronounced softening also resulted in the minimum strength values not being achieved for certain cooling time ranges.

Mechanical characterization of gypsum mortars with waste from the automotive sector

The construction sector is one of the main industries generating greater environmental impacts. In this sense, the European Commission is forcing the sector to implement alternative measurement and strategies to tackle this situation and bring the sector to a circular economy. One of the adopted measures is the use of recycled materials to produce construction materials and products. In this sense, many scientific works have been conducted analyzing the incorporation of different waste categories in gypsum products. In this sense, the main objective of this research is to characterize new gypsum-based materials that incorporate waste from the automotive sector. For this, mixed waste (containing polyurethane, cardboard and fiberglass) obtained during the production of automobiles’ backboards was used. A total of 171 specimens were produced incorporating different percentage and size of mixed waste. These specimens were tested according to the bulk density, superficial hardness, and flexural, compressive and bonding strengths. Results show that it is possible to incorporate up to 11% of mixed waste overpassing the minimum strength values established by the regulations. In addition, the lightness of the material and its compression and flexion behavior improved considerably compared to the reference specimens without any waste addition.

Co-valorization of sediments incorporating high and low organic matter with alkali-activated GGBS and hydraulic binder for use in road construction

This study investigates the valorization of dredged sediments containing high and low organic matter (OM) content with alkali-activated ground granulated blast furnace slag (GGBS) and conventional hydraulic binders (HB). The objective is to develop a sustainable material with the necessary qualities for road construction. Research is conducted on dredged sediments from the French port of Cherbourg (CHER-ALL sediments) and the dam in the Maurienne Valley of France (MOR-ALL sediments), with high and low levels of OM content, respectively. After the determination of physico-chemical and mineralogical characteristics, high organic CHER-ALL sediments were first valorized using conventional HB and then co-valorized using low carbon footprint alkaline activated byproducts (AAB). The alkali activation of the byproduct (GGBS) was performed with a chemical activator named NeoliX. AAB and HB were utilized to treat the dredged sediments to compare their mechanical performances as well as environmental impacts. In terms of mechanical performance, the obtained results revealed that AAB outperformed traditional HB, and concerning the environmental impacts, byproducts have no carbon footprint except for their transportation. As a consequence, AAB has also been utilized to co-valorize the sediments from the Maurienne dam (MOR-ALL sediments) as well. AAB co-valorization of these two sediments (CHER-ALL and MOR-ALL) with varying degrees of OM content facilitates an understanding of the effects of OM concentration on mechanical properties. The high OM content of the CHER-ALL sediment (>17%), regardless of the proposed mixing with traditional HB, proved to impede the valorization, since the 28-day UCS did not exceed 1 MPa. The CBR as well as ultimate tensile strength (UTS) testing confirms the reported trends from the UCS experiments. In addition, the presence of a high OM concentration significantly decreased the mechanical properties of dredging sediments co-valorized with AAB. However, depending on the mass percentage of sediment (wt%) in the mix design, it was achievable to attain the required minimum strength value of 1 MPa with 30% and 70% of CHER-ALL and MOR-ALL sediments, respectively. Even if the OM content of sediments is high, alkaline activation can be employed to co-valorize them, as demonstrated by these encouraging results. The quantity of sediment to be co-valorized is depend upon their OM content.

Treatment of Clay with Oil Palm Fibre Ash and Rice Husk Ash Mixture for Burnt Clay Bricks Production

The current study examines the use of oil palm fibre ash (OPFA) and rice husk ash (RHA) mixture in the treatment of A-6 Makurdi clay for burnt brick production. The results show that the compressive strength of 9.4 MN/m2 for burnt untreated brick increased to 10.86 MN/m2 for burnt 2%OPFA+2%RHA treated brick. The corresponding water absorption of 14.9% for the burnt untreated brick increased to 16.2% for burnt 2%OPFA+2%RHA treated brick. The strength value of 10.86 MN/m2 is greater than 10.3 MN/m^2 which is the minimum strength value for negligible weather (NW) conditions. The water absorption of 16.2% is less than 17%, 22% and ‘no limit’ which are the maximum values for severe weather (SW), moderate weather (MW) and NW respectively. Based on combined strength and water absorption criteria, burnt bricks production with 2%OPFA+2%RHA treated A-6 Makurdi clay is adequate for use as a load-bearing brick in wall areas of NW condition.

ESTIMATION OF STRENGTH CHARACTERISTICS OF THE ZIRCONIUM E125 ALLOY MATERIAL IN THE ZONE OF LOCAL THERMAL EXPOSURE

The paper presents the results of mechanical tests to determine changes in the strength characteristics of the material of zirconium alloy E125 after local thermal exposure. Dependences of the strength characteristics of the material of the E125 alloy on the hardness are determined. The maximum and minimum values of strength in the zones of reflow and heat exposure have been determined. An assessment of the change in the geometric parameters and the hardness of the heat- affected spot from the modes of arc action and the conditions of subsequent cooling is carried out.

Alkali-Activated Hybrid Concrete Based on Fly Ash and Its Application in the Production of High-Class Structural Blocks

This article reports the production and characterization of a hybrid concrete based on the alkaline activation of a fly ash (FA) of Colombian origin, which was added with 10% Portland cement (OPC) in order to promote the compressive strength development at room temperature. The alkali-activated hybrid cement FA/OPC 90/10 was classified as a low heat reaction cement (type LH), according to American Society of Testing Materials, ASTM C1157; the compressive strength was of 31.56 MPa and of 22.68 MPa (28 days) at the levels of paste and standard mortar, respectively, with an initial setting time of 93.3 min. From this binder, a hybrid concrete was produced and classified as a structural type, with a compressive strength of 23.16 MPa and a flexural modulus of rupture of 5.32 MPa, at 28 days of curing. The global warming potential index (GWP 100), based on life cycle analysis, was 35% lower than the reference concrete based on 100% OPC. Finally, its use was validated in the manufacture of a solid block-type construction element, which reached a compressive strength of 21.9 MPa at 28 days, exceeding by 40.6% the minimum strength value established by the Colombia Technical Standard, NTC 4026 (13 MPa) to be classified as high class structural blocks.

Study of the incorporation of fabric shavings from the clothing industry in coating mortars

The increase in waste generation in the textile and clothing industry is a reflection of population growth. In Brazil, only 20% of this waste is reused. The construction industry is one of the sectors that are able to absorb solid waste from various industrial activities, seeking alternatives for use and for waste valorization. Correspondingly, in this work, coating mortars were produced with the incorporation of fabric shavings (cement: hydraulic lime: sand at a ratio of 1:1:6 by mass), and evaluated them as reinforcement or thermal insulation materials. The waste was shredded manually to emulate the fibers that exist in the market. To analyze the influence of waste on the coating mortars properties, a 32 factorial design was performed, wherein the yarn content varied (at 1, 2, and 3% in relation to the binder mass) and the length varied at 1, 2, and 3 cm. The mortars that contained the yarns were experimentally evaluated based on flexural tensile strength and tensile adhesion strength tests. The best composition (yarn content of 3% and length of 3 cm) was subjected to a) thermal tests at 40 °C and 60 °C, b) mechanical, and c) physical tests, and their outcomes were compared with those of the reference sample (without waste). When waste was introduced in the mortars, the water/binder ratio increased to maintain the same consistency index. In the adhesion test, the mortars with waste adhered to the substrate and reached the minimum strength value required by the technical standards of 0.30 MPa. The flexural tensile strength was also higher than the established 1.0 MPa. With the exception of tensile adhesion strength, the mechanical strength of the mortar with the fabric yarns was less than that of the reference mortar. The mortar with the added waste yielded a satisfactory performance in thermal tests at 60 °C.

Structural Mechanics Aspect of Strength of Composite Reinforcement

When operating in wet and corrosive conditions, composite reinforcement is in some cases an effective substitute for the suitable steel reinforcement. However, many questions related to its design, production and operation are insufficiently studied. The aim of the work is to create a methodology and carry out a comparative structural and mechanical analysis of strength indexes when working under load of coils and a bar of composite construction reinforcement. A method has been developed for analyzing the loading capacity of composite reinforcement according to the criteria of strength at rupture of a bar, as well as shear strength and bearing strength of its braid coils. Analytical and numerical modeling of conditions of equal strength of structural elements of composite construction reinforcement was carried out. Theoretically substantiated the assumption of a relatively low loading capacity of the braid coils in comparison with the loading capacity of the reinforcement bar. A predictive estimate of the conditions for ensuring the uniform strength of the bar for breaking and braid coils for shear and crushing by the method of lower estimation (for the minimum values of strength) has been carried out using the example of composite reinforcing bars produced by the industry of Republic of Belarus. In conclusion, results of work are formulated and it is noted that the results can be used by manufacturers and consumers of construction composite reinforcement, also in the educational process in the training of engineering personnel for the construction profile.

Influence of Wood and Plastic Waste as Aggregates in Gypsum Plasters

Large amounts of waste are generated each day in the world, being a major concern for the EU28, who establish waste management as a priority line of work within the Horizon 2020. Construction sector is one of the largest residues generators. In that sense, architects and civil engineers should give an answer to solve that environmental problem. One of the options is to reuse waste for the generation of new materials and products for construction. In this research, wood waste (sawdust) from demolition works and polycarbonate waste have been used as aggregates to generate new gypsum plasters. Different percentages of additions (5, 10, 20 and 40%) for each type of waste have been conducted to develop the gypsum composites. Physical (density and thermal conductivity) and mechanical (flexural and compressive strength) properties of the new plasters have been measured using the procedure regulated by standards, comparing them with the reference material values (commercial gypsum without aggregates). The results of the tests show that lighter composites have been obtained when the percentage of waste increased for both type of aggregate. This lightening is higher in composites with wood waste than in those with plastic at the same percentage of addition. Furthermore, an improvement in the thermal conductivity of the plasters have been achieved. On the other hand, a decrease on the mechanical properties of the composites, with higher percentages of additions, have been obtained. For all the cases, the minimum strength value required by standards have been achieved. As a conclusion, lighter gypsum composites with enhanced thermal properties have been obtained, achieving in all the cases an acceptable flexural and compressive strength.

Assessment of Isometric Pulls Strength of Industrial Cart Pullers -An Electromyography Study from an Apparel Manufacturing Industry

Manual material handling and occupational tasks demanding physical push-pull activities are very common in various industrial settings regardless of automation. These activities may become the cause of fatigue, accidents and/or different occupational hazards if not properly focused to balance workload as per physical strength and stamina of the worker. This cross-sectional study was conducted to assess the isometric pull strength of apparel cart/trolley pullers and muscular activity of upper limbs. Jackson strength evaluation system was used to measure isometric pull strengths while IXTA Data Acquisition System to measure and analyze the muscle activity. The experiments were conducted with twenty work-in-process (WIP) manual material handlers of an apparel manufacturing industry. Electromyographical (EMG) data of muscle activity was collected by placing electrodes on pronator teres, brachial biceps, pectoralis major and lower trapezius muscles during the pull tasks. The results show that torso pull in seated posture has the maximum isometric average value of 62.20 ± 5.91 kg while arm lift has the minimum strength value of 37.10 ± 4.61 kg. Assessment of muscle fatigue caused by pulling force is important in determining job severity of workers and mitigating occupational injuries which help in balancing workloads for effective management.

Structural Safety of Photovoltaic Modules in the Building Envelope

The mechanical performance of photovoltaic modules has not been adequately characterized for use as glazing product in the building envelope. As a result, the modules are subject to individual approval by the building authorities in many building-integrated applications. This paper presents experimental research on glass based photovoltaic modules, analyzing their mechanical properties in comparison with regulated construction products. The focus is on the influence of photovoltaic thin-film coatings on the bending strength of the float glass used as a substrate or superstrate and on the post-breakage behavior of glass-glass modules. The four-point bending test according to EN 1288-3 was modified in terms of specimen dimensions in order to test full-size photovoltaic glass panes. The modified set-up was verified as a suitable and simple test method to determine and confirm strength values. Edge ablation was found to reduce glass strength rather than the PV coating and cell scribing processes, but the reduction is less than 10 % and the minimum strength value of float glass can still be met. Residual strength testing of glass-glass photovoltaic modules in different load and temperature scenarios showed that the integration of crystalline silicon cells as well as thin-film solar cells improves the post-breakage behavior of glazings. A critical point may be mechanical failure within the layers of thin-film cells on glass associated with the potential danger of broken glass pieces falling down. Standard glass-glass module configurations appear to provide the same or higher residual strength performance as laminated safety glass, if the interlayer material is approved for use in laminated safety glass.

The Effect of Fe-Rich Intermetallics on the Weibull Distribution of Tensile Properties in a Cast Al-5 Pct Si-3 Pct Cu-1 Pct Fe-0.3 Pct Mg Alloy

A comparison was made between the tensile properties of an Al-5 pct Si-3 pct Cu-1 pct Fe-0.3 pct Mg (319-type) alloy in the as-cast condition. The alloy was either unmodified or modified with Mn or Sr. The additions of 0.6 wt pct Mn, or 0.9 wt pct Mn, or 300 ppm Sr were made. All modifying additions increased the average and decreased the scatter in tensile strength, and increased elongation, with the Sr addition being most effective among the three. Fractographic examinations showed that the β phase, the polyhedral α phase, and porosity appear to be the main defects responsible for failure. The distribution of tensile strength has been quantitatively assessed using both two- and three-parameter Weibull distribution functions. In the two-parameter Weibull analysis, the high Weibull modulus (46) achieved by Sr modification is due to its binary effect on eutectic silicon and β platelets. Reservations about potentially misleading implications of the two-parameter approach are explored. The three-parameter Weibull analysis provides new information. In particular, minimum values of strength below which the material is extremely unlikely to fail are found. These values again show the clear benefit of Sr addition. The results are explained by the effects of modifying agents on the microstructure.

Experimental studies on the adhesion strength of a polymer-metal bond depending on the contact zone geometry

Theoretical investigation of the stress-strain state at special points of constructions, e.g., in adhesion joints, has demonstrated that the stress state in the contact zone strongly depends on the configuration of the zone. In order to verify these results, some experiments were carried out. Cylindrical polymer specimens having a circular groove at one of its ends were cemented to steel mushrooms and tested for abruption in tension and cantilever bending. The experiments showed that the adhesive strength depended on the profile of the joint and had a maximum at the optimum value of the angle of the joint and a minimum when the groove was absent. The ratio between the maximum and minimum strength values was 1.5 in tension and 2.5 in bending. The greater effect in the latter case can be explained by the high gradient of the stresses in bending. The experimental results confirmed the possibility of controlling the adhesive strength by changing the contact geometry in accord with the stress-strain calculations.

Studies on direct compression of tablets XXI. Investigation of bonding mechanisms of some directly compressed materials by strength characterization in media with different dielectric constants (relative permittivity)

Three substances with varying properties regarding compactability and volume reduction mechanisms were compressed both in air under ambient conditions and in liquids with different dielectric constants. The relative importance of bonding with intermolecular forces compared with that with solid bridges and mechanical interlocking was evaluated by comparison of the radial tensile strengths of compacts under ambient conditions vacuum, and in liquids with increasing dielectric constant. All investigated materials increased in radial tensile strength in vacuum, which corresponds to a medium with a dielectric constant of unity. The increase was greater for materials with a high surface area, indicating that the increase in strength in vacuum is primarily caused by increased surface interactions due to removal of adsorbed water vapor and surface contaminations which act as a filter, reducing bonding with intermolecular forces in the compact. An increase in the dielectric constant of the liquid generally decreased the radial tensile strength of the investigated compacts. The compact strength decreased monotonically down to a plateau value or to zero. For all materials, these minimum values were obtained at dielectric constants between 10 and 20. It is suggested that the remaining strength seen in the plateau values is predominantly due to solid bridges or interlocking mechanisms. The difference between the radial tensile strength in vacuum and these minimum strength values obtained in liquids was thus used as an indication of the amount of bonding with intermolecular forces. Bonding with intermolecular forces seems to be the dominating bonding mechanism for all the investigated materials. Bonding with solid bridges and mechanical interlocking contributes to a minor degree to the compact strength of the model substances except for the coarse fraction of sodium chloride. The results obtained support the idea that pharmaceutical compacts can generally be regarded as agglomerates of primary particles that are mainly attracted to each other by bonding with intermolecular forces.

Probability nature of the size effect in yarn strength

The basic reason for the size effect in yarn strength is nonuniformity of the yarns in linear density and strength and the associated statistical period of repeatability in minimum strength values.