Increase In Initial Strength Research Articles

Effects of burnt sawdust ashes from timber species on the strength properties of laterite-interlocking blocks

The most basic problem facing man is shelter, apart from food. This problem is acute in Ghana and other developing countries due mainly to the high growth rate of the population, inflation, unemployment and poor economic resources. Today in Ghana both middle and low income earners can hardly afford their own houses. From one point of view one can see that some of the materials used in building are of good quality and can last. The study aimed to partially replace ordinary Portland cement (oPc) with burnt sawdust ash (BSDA) from different timber species (Wawa, Mansonia, Teak, Odum, Ceiba, Essah and Mahogany) in making interlocking laterite blocks by replacing 0–30 wt %. Mix proportion was 1:8 (cement + BSDA: laterite) with a 0.60 water-to-cement ratio. 528 specimens of size 185 mm × 220 mm × 120 mm were produced and cured at normal temperature and humidity under shady and sunny conditions for 7, 14, 21 and 28 days. Compressive and tensile strengths were subsequently evaluated. However, an initial strength increase was observed with curing time for specific wood species (Wawa, Mansonia, Teak, Odum, Essah, Ceiba, and Mahogany). Notably,Wawa, Mansonia and Odum ash exhibited superior strength performance at 10–20% replacement levels, potentially satisfying relevant standards for load-bearing wall construction. This research suggests that up to 10% replacement with Wawa, Mansonia or Odum BSDA presents a promising eco-friendly approach for partially substituting oPc in LIB production.

The effect of changing constituents on tensile mechanical properties of HfNbTaTiZr high entropy alloy: A molecular dynamics study

The recent trend of high-entropy alloys (HEAs) was studied extensively for their promising mechanical properties, but individual constituents' effects have remained unexplored. In this work, the effects of changing the percentage of elements of HfNbTaTiZr-HEA on the mechanical properties were analyzed during uniaxial tension using molecular dynamics simulation. The tensile strength and modulus of elastic properties of the samples were analyzed. It was found that adding Nb or Ta up to 10 % (i.e. Nb10/Ta10) in the high entropy alloys increased the ultimate tensile strength (UTS) from 2.9 GPa in the base alloy to 3.8/3.9 GPa (Nb10/Ta10) respectively, but further increment of these elements to 30 % resulted in a downgrade of UTS to 2.7 GPa. Similarly, the modulus of elasticity increased from 117.7 (±3) GPa in the base alloy to 137.7/129 (±3) GPa (Nb10/Ta10) respectively, but fell to 112–115 GPa upon further increment. The initial increase in strength could be due to the solid solution strengthening mechanism. However, further increases in these elements might hinder the development of a homogeneous solid solution because of differences in atomic size and crystal structure, which could ultimately reduce the alloy's strength. However, the effect of Ti and Zr follows an opposite trend as compared to Nb and Ta. Furthermore, the optimum composition of HEAs alloys was analyzed using a surface-contour plot and suggests minimizing the inclusion of Ta for maximizing the UTS, E, and %Elongation. Also, the high-temperature behavior of the optimized HEA's alloy was analyzed which showed a deterioration in properties at elevated temperature. The fracture evolution of the samples showed cup and cone-type fractures propagating under strain, the linear thermal expansion coefficient of HfNbTaTiZr-HEA was also calculated and found closer to the literature value.

Mechanical properties, microstructure and GEP-based modeling of basalt fiber reinforced lightweight high-strength concrete containing SCMs

The pressing need to address recent global climate changes calls for replacing high-carbon-emitting cement with environmentally friendly materials that retain the strength and properties of conventional concrete. This study explored the mechanical properties of lightweight concrete (LWC) incorporating shale aggregate and basalt fibers alongside a partial replacement of environmentally detrimental cement with pozzolanic materials like fly ash (FA), blast furnace slag (BS), and silica fume (SF) up to 30 %. Twenty mix designs were developed to examine their mechanical properties and microstructural characterization. It was also observed that SF outperformed other industrial byproducts and gave better strength with the optimum replacement of 20 % cement, achieving 102.6 %, 105.6 % and 109.5 % of the control mix compressive, flexural, and split-tensile strength, respectively. However, a further increase of up to 30 % decreased strength. FA and BS resulted in lower strength than the control sample and other byproducts-based mixes, with compressive strength decreasing by 4 %–20.5 % at replacement levels of 10 %–30 %, respectively. BS resulted in an initial increase in strength at 10 % replacement but decreased by 10.8 %–21.6 % at higher levels. This trend was similar for flexural and tensile strengths. However, adding basalt fibers resulted in higher strength compared to non-fiber mixes and increased the strength of LWC by up to 25.2 %. The micromorphology and pore structure study indicated that the high-performance paste and fibers bridging effect were crucial for high strength. Gene expression programming (GEP) based modeling, validated against our own experimental results, was employed to predict the outcomes, demonstrating strong correlation coefficients for compressive, flexural and tensile strength (0.9430, 0.9609 and 0.9353, respectively). Additionally, SHapely Additive exPlanations (SHAP) analysis was used to assess the impact of each input parameter, highlighting the positive effects of the water-to-binder ratio and lightweight aggregate on the LWC's mechanical properties. This study is novel in its comprehensive examination of the combined impact of SCMs, shale aggregate and basalt fibers on the performance of LWC, a synergy not extensively explored in prior research. Furthermore, a novel generalized constitutive model was developed, and a SHAP analysis was performed to help design an efficient mix design to enhance the mechanical performance of LWC.

REVIEW: AN EXPERIMENTAL STUDY ON EFFECT OF NANO MATERIALS ON STRENGTH OF CONCRETE AND PLANE STRESS ANALYSIS USING ANSYS SOFTWARE

These days, making efficient and cost-effective use of resources has taken precedence. The main ingredient in concrete, cement has been under criticism in recent years for the quantity of CO2 released during production. Although cement has better mechanical properties, it hasn't been able to live up to the expectations in terms of durability. Owing to cement's shortcomings, scientists started looking into additives that would enhance concrete's qualities while also making it stronger and lighter. Fly ash, silica fume, and other micro particles were added to cementitious materials to improve their compactness, strength, and durability. These additives were also selected because they are eco-friendly by products of industrial waste that may be handled ethically. Fly ash has significant disadvantages because it is not good for initial strength increase and setting time. Because silica fume affects cementitious material performance, researchers have recently become interested in combining it with ceramic waste and rice husk ash. A more effective way to utilize rice husk ash, a by-product of rice cultivation, would be to replace 10% to 15% of cement. Studies have shown improvements in the durability performance of recycled ceramic waste concrete and rice husk ash concrete. There are issues since the RHA production process is quite time-consuming. With the discovery of nano-particles (NP) smaller than 100 nm, researchers have advanced the field of nanotechnology to new levels. The mechanical properties of many materials, including polymers and cementitious materials, can be enhanced by NP. NP is also helpful in the fields of food, engineering, and medicine. This led researchers to investigate the effects of nano-silica (NS) on concrete in further detail. Nano materials can improve the compressive strength and ductility of concrete. In this project an effort will be made to increase the compressive strength of concrete using Nano materials and waste product like GGBS. Also plane stress analysis of concrete cubes and cylinders is to be done using Ansys Software to find deformation, principal stresses and shear stresses. Keywords: Nano –Silica, Nano Titanium dioxide, Ansys, GGBS, Compressive strength

Tribological and texture analysis in Twin-roll casting 2060 Al-Li alloy

In this work, the wear behaviors of a 2060 Al-Li alloy prepared by the twin-roll casting (TRC) process was analyzed and supplemented with coupling simulation calculations. As the load increased from 2 N, 5 N, 10 N, and 20 N at room temperature, the friction coefficient decreased due to the oxidation lubrication triggered by heat accumulation, which was calculated via the simulation; the wear volume decreased; and the decrease in wear volume rise rate was a result of dynamic recrystallization and grain rotation. Observing the grain rotation and analyzing the texture evolution law during wear tests with scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD) was an innovation. To support the rotation behavior, a method for calculating the Schmid factor of rotating grains was developed. As the load rose, the R-Cube {001} 〈110〉 texture rotated to the rotating cube {001} 〈310〉 texture towards the α-fiber line. The modification decreased the maximum Schmid factor along the sliding and rolling directions, indicating an increase in initial strength and wear resistance. In addition, at a 2 N load, the TRC-3 sample with higher substructure and deformation texture exhibited less wear volume than the TRC-6 sample.

Stability of the microstructure and elevated-temperature mechanical properties of additively manufactured Inconel 718 superalloy subjected to long-term in-service thermal cycling

The present study investigates the thermal stability of the additively manufactured Inconel 718 (IN718) under a long-term thermal cycling exposure, similar to what is encountered in aircraft turbine engines, up to 3000 h. Before thermal cycling, the IN718 parts were heat-treated using two conditions designated, respectively, 2.5H and 4H. The results show that, after the simulated in-service thermal cycling conditions, the 2.5H and 4H treated samples exhibited initially a slight increase in their tensile (TS) and yield strengths (YS) at 650 °C to reach their maximum values after 500 and 1000 h, respectively, and then gradually decreased with further thermal cycling time to reach their lowest values after 3000 h. The microstructural analysis and the X-ray diffraction (XRD) results revealed that a slight initial strength increase is mainly due to a larger precipitation of γ′′ and inter-granular δ-phase during a relatively short-term thermal cycling exposure, whereas the prolonged thermal cycling time resulted in an undesired phase transformation of the metastable γ′′ to intra-granular δ-phase which adversely affected the mechanical properties. However, comparing the tensile results of both treated conditions revealed that the 4H treatment effectively delayed the deteriorations of the material strength until after 2000h as compared to the 2.5H condition for which the strength deterioration occurred after 1000 h due to a slower phase transformation of γ′′ into δ-phase in the former condition. Considering the thermal stability during in-service exposure, it was found that the 4H treated samples demonstrate a higher strength stability than their 2.5H treated equivalents, since after a thermal cycling exposure for 3000 h, the TS and YS values of the former decreased by only 3.3 and 1.3% of the initial state, respectively, as compared to 5.3 and 3.8%, for the latter.

Freeze–Thaw and Salt Crystallization Durability of Silica Acid Ester Consolidated Porous Limestone from Hungary

The durability of consolidated highly porous limestones was tested after salt and freeze–thaw cycles. Three porous limestone lithotypes that were commonly used in construction in the Central-European region during previous centuries were selected for the tests. Specimens of Miocene limestone were consolidated with four different types of ethyl silica-based consolidants (KSE 100, KSE 300, KSE 300 E, KSE 300 HV). After consolidation, the samples were exposed to freeze thaw cycles and salt crystallization tests. Water saturation under atmospherically pressure, capillary water absorption and splitting tensile strength were measured on treated and untreated samples to assess change attributed to consolidation in the open porosity and mechanical parameters. The increase in the tensile strength of the medium-grained samples was higher than that of the consolidated fine-grained lithotypes. The effect of consolidation treatment was very different in terms of pore-size distribution as obtained by Mercury intrusion porosimetry (MIP). Untreated and consolidated samples were subjected to 10 cycles of sodium sulphate crystallization (EN 12370) and 10 freeze–thaw cycles (EN 12371) tests. Experiments concluded that in addition to the initial strength increase after the conservation, the modified pore structure is the crucial factor to evaluate the long-term efficiency of stone conservation.

Mechanical Properties of Mortars Based on Roman Cement with the Addition of Power Plant Fly Ash

Roman cement is a historic hydraulic binder, prepared by firing of limestone with high proportion of clay minerals, usually at temperatures below the sintering point. The firing temperatures of Roman cements range from 800 to 1200°C. At present, this binder is considered to be a promising material with a low carbon footprint and a long lifetime. The properties of Roman cement are influenced by many factors, especially raw materials composition and firing conditions. On the other hand, a disadvantage of mortars based on Roman cement is a slow increase of initial strength. In this paper, the influence of power fly ash admixture on the dynamics of initial strength increase was experimentally investigated. The characteristics of mortars with admixtures were compared with the properties of reference mortar without admixtures. The Roman cement Vicat Prompt TM Natural Cement (manufactured by Vicat SA, French company) was used as a binder. Based on the results of the experiment it can be stated that mortars with the admixture of power plant fly ash show higher dynamics of the increase of initial strengths than the reference mixture.

Influence of Fly Ash Additive on the Properties of Concrete with Slag Cement.

This paper presents research on the impact of fly ash addition on selected physical and mechanical parameters of concrete made with slag cement. Experimental tests were carried out to measure the migration of chloride ions in concrete, the tightness of concrete exposed to water under pressure, and the compressive strength and tensile strength of concrete during splitting. Six series of concrete mixes made with CEM IIIA 42.5 and 32.5 cement were tested. The base concrete mix was modified by adding fly ash as a partial cement substitute in the amounts of 25% and 33%. A comparative analysis of the obtained results indicates a significant improvement in tightness, especially in concrete based on CEM IIIA 32.5 cement and resistance to chloride ion penetration for the concretes containing fly ash additive. In the concretes containing fly ash additive, a slower rate of initial strength increase and high strength over a long period of maturation are shown. In accordance with the presented research results, it is suggested that changes to the European standardization system be considered, to allow the use of fly ash additive in concrete made with CEM IIIA 42.5 or 32.5 cement classes. Such a solution is not currently acceptable in standards in some European Countries.

Comparative study on utilization of different types of municipal solid waste incineration bottom ash for clinker sintering

In this study, two types of municipal solid waste incineration (MSWI) bottom ash (BA) (MSWI-BA-A, water quenched, MSWI-BA-B, natural cooling), are utilized as alternative materials for clinker sintering. Fixed clinker modulus (lime saturation ratio = 0.90 ± 0.01, silica modulus = 2.6 ± 0.1 and alumina modulus = 1.5 ± 0.1), designed gradient addition ratio of MSWIBA (0, 3%, 6%, 9% and 12%) and same sintering temperature (1723.15 K) are adopted to conduct the experiments. Raw materials are characterized by XRF, X-ray diffraction and differential thermal analysis. Clinkers are analyzed and evaluated by XRF, X-ray diffraction, petrographic analysis, compressive and flexural strength tests and toxicity characteristic leaching procedure. The major difference of the two types of MSWIBA is LOI value which is supposed to be the most probable reason for huge difference between liquid phase formation temperature variation and incremental introduction of MSWI. MSWI-BA-A increases liquid phase formation temperature. Liquid phase formation temperatures and MSWI-BA-B samples addition ratios nearly present negative linear correlation. All clinkers sintered with addition of MSWIBA slightly reduce water demand for normal consistency. MSWIBA addition poses relatively obvious influence on initial setting time and little effect on final setting time. There is an increase in initial strength and a decrease in 28-day strength of clinkers sintered with MSWIBA, 28-day compressive strength decreases with the incremental introduction of MSWIBA. Distinct characteristics, such as free lime, periclase, orthorhombic tricalcium aluminate (C3A) crystal and secondary Belite crystal, are observed by petrographic analysis. MSWIBA is significant source of free lime and periclase in clinkers. Incremental input of alkali introduced by MSWIBA influences clinker sintering and mineral crystallinzation, further results in orthorhombic C3A crystal and indistinct Alite edge caused by corrosion. Leaching concentration of heavy metals from mortars prepared with the sintering clinkers is lower than corresponding concentration of the Chinese National Standard GB 30760-2014.

CEMENT PASTE CONTAINING MICRONIZED RECYCLED CONCRETE - INFLUENCE OF HARDENING ACCELERATORS ON THE MODULUS OF ELASTICITY

The article deals with the selection of a suitable hardening accelerator for cement composite material for mass production of masonry blocks. The blocks contain cement and finely ground recycled concrete in ratio 1:1. Three different hardening accelerators in different quantity were tested for possibility of fast removing formwork. The dynamic modulus of elasticity was measured by non-destructive resonance method to determine the initial strengths. The modulus of elasticity was measured 7 and 12 hours after sample production to determine the increase in initial strength. Subsequently, the modulus of elasticity was measured at 1, 7, 14, 21 and 28 days after production of the test specimens. The resulting moduli of elasticity were compared with reference samples.

Experimental study of the effect of submersion time on the strength development of freeze bonds

Freeze bonds have been found to influence the mechanical properties of ice rubble and ridges, and it is therefore important to study the fundamental physical properties affecting these features. The shear strength of freeze bonded ice blocks has been investigated through a series of asymmetric four point bending (AFPB) experiments for different submersion times and initial ice temperatures. Ice blocks were subject to a confinement of 25 kPa and were sheared at an actuator rate of 5 mm/s. Effects of submersion time on shear strength of freeze bonds was investigated by varying the submersion time from 1 min to 14 days, for two initial ice temperatures of −18 °C and −10 °C. Shear strength values measured are believed to be dominated by two concurrent mechanisms. Thermal bond growth is the first mechanism, where an initial increase in strength with submersion time is observed, reaching a peak after four (4) minutes of submersion time and gradually decreasing to a constant value. Sintering-creep bond development is the second mechanism that significantly influences the bond strength in submersion times longer than 24 h, where the strength increases and eventually asymptotes to the strength of solid ice. An empirical equation which estimates the bond strength as a function of submersion time and initial ice temperature is developed.

A study on strength characteristics of concrete under variable temperature curing conditions in ultra-high geothermal tunnels

The heat conduction of rocks and the ventilation conditions in high geothermal tunnels always result in dynamic changes of curing temperature and humidity of concrete materials, which may further significantly affect the concrete’s performances. According to the field tests on both environment and concrete’s temperature and humidity, a new model for concrete curing was proposed, which can really reflect the curing process of concrete in high geothermal tunnels. Based on the model, concrete specimen tests were carried out in different conditions where the initial curing temperature was set to 40 °C, 50 °C, 60 °C, 70°C and 80 °C, respectively, and the relative humidity (RH) was maintained at 25%, 55% and 95%. The results indicate that the actual high curing temperature of concrete usually decreases with time and tends to become stable 7 days after casting. Though the initial high temperature causes a rapid growth of the concrete strength at the early age, an insufficient strength over the long-term can also be leaded. While RH has a beneficial effect on the increase of initial strength and can effectively reduce the loss of long-term strength caused by the high temperature. All of the temperature, humidity and their coupling effect can influence the strength, and the influence levels follow the order: T&RH < T < RH. Finally, a new prediction model to predict the strength of concrete used in high geothermal tunnels was proposed and verified by the field tests.

Cement Bonded Particle Boards with Different Types of Natural Fibres—Using Carbon Dioxide Injection for Increased Initial Bonding

The effect of CO2 injection on initial strength increase and hardening of cement-fibre mix in a cement bonded particle board (CBPB) production was evaluated. Different cement contents, formation pressure and types of fibres were considered. The initial strength increase with CO2 injection is so much faster than this caused by conventional hydration that the produced samples do not need additional curing before they can be stored. Similar strength and stiffness values as in conventional products on the market are gained with lower cement content for similar types of fibres. Visual inspection of board surfaces aged for 13 years in a harsh exterior environment as well as comparison of strength and stiffness values for these boards when new and after ageing, gives a very satisfying result. The combined effect of the above discussed gains results in markedly increased productivity at lower cost and lower environmental impacts than is possible in traditional CBPB production.

Root biomechanical properties during establishment of woody perennials

Background and aimsSoil bio-engineering using vegetation is an environmentally friendly solution to stabilise soil slopes. This study investigates tensile strength, Young’s modulus, and root diameter relationships for establishing woody perennials. MethodsSpecimens of ten woody European shrubs and small trees were transplanted into sandy loam soil to establish for six months. Root tensile strength and Young’s modulus were measured as well as the root length-diameter distribution. The effect of root water status on root diameter was evaluated for Scotch Broom. ResultsMore than half of the root length for all species was thinner than 0.5mm diameter. Typical tensile strengths were <40MPa, with Young’s modulus <600MPa. Negative power relationships between root strength and root diameter existed only for Gorse and Spindle, whilst Blackthorn, European Box and Holly showed slight increase in tensile strength with diameter. Hawthorn, Hazel and Privet showed rapid initial increase in strength with diameter followed by strength decrease with diameter, post-peak. Young’s modulus was linearly related to tensile strength for all ten species (P<0.001; R2 values 17%–64%). Root diameter, investigated for Scotch Broom, depended strongly on root water potential and root water content by mass. Root water content could influence considerably the calculations of tensile strength. Discussion and conclusionRoot tensile strength-diameter relationships often do not follow a negative power law, and depends strongly on taxa. Young’s modulus was strongly related to tensile strength of roots for certain species. Water status of roots strongly influences root diameter and hence strength and Young’s modulus properties, and must be controlled carefully in experiments.

High temperature behaviour of hybrid steel–PVA fibre reinforced reactive powder concrete

Reactive powder concrete (RPC) with dense microstructure are found to perform poorly at elevated temperatures due to a build-up of pore pressure that causes explosive spalling. This paper presents the results of an experimental investigation of the behaviour of six RPC mixes containing hybrid steel and polyvinyl alcohol (PVA) fibres, following exposure to high temperatures up to 700 °C. Residual compressive strength, static elastic modulus and ultrasonic pulse velocity measurements were carried out for all the RPC mixes. A mix containing hybrid steel–PVA fibre is proposed as suitable for high-temperature applications based on these results. Further tests were conducted for the mix at a hot state using a specially designed furnace–loading frame assembly. The hot-state elastic modulus, free thermal strains (FTS) and transitional thermal creep (TTC) were measured at the hot state. Residual compressive strength results for all the mixes indicated an initial increase in strength up to 300 °C, followed by a drastic drop. No apparent changes in elastic modulus and ultrasonic pulse measurements were observed till 300 °C, after which both dropped sharply. RPC containing only either steel fibres or only PVA fibres showed some form of instability, which was explosive in some cases. RPC with no fibres was also susceptible to explosive behaviour; however, the addition of hybrid fibres seemed to have beneficial effects. A mix containing equal volumes of steel and PVA fibres occupying a total fraction of 2 % by volume was found to give the best results. The FTS of that mix was similar to that of siliceous aggregate concretes, and the TTC was significant above 250 °C.

Effect of environment change on the strength of cement/lime treated clays

The field strengths of cement/lime treated clays were investigated in the Ariake Sea costal lowlands. The deposition environment of the investigation location is reconstructed and compared to the present ground environment. The mechanism of the ground environment change and its effect on the strength of cement/lime treated soil are discussed. The strength development of improved soil using cement and lime in different curing environments was investigated in the laboratory for studying the effect of environment change on the strength also. It has been found that the strength deterioration of improved soil in deep mixing method is due to 1) the ground environment change due to the secondary oxidation which results in low pH value and high organic content, and 2) the formations of the porous structures result from the elution of the calcium ions. Also, it has been found that the initial strength increase of the improved soil is related to the dissolved silica and that the dissolution of the silica in clay minerals needs long time. When examining the long-term strength for preventing strength degradation, the effect of environmental change has to be considered. The importance of measuring pH and oxidation-reduction potential (ORP) of the ground for cement/lime solidification method is explained.

Weakening of Alkali‐Activated Metakaolin During Aging Investigated by the Molybdate Method and Infrared Absorption Spectroscopy

Aluminosilicate gels were synthesized by mixing metakaolin with potassium water glass solution. Mechanical strength values showed a strong increase between 25 and 100 h but decreased again above 200 h for aging at 25°C. A similar curve was observed during aging at 50°C but the maximum strength shifted to shorter time. Aging at 90° and 130°C revealed only the decreasing wing in mechanical strength. The strengthening and weakening during aging at 25°C were further investigated by the molybdate method and infrared absorption spectroscopy. The results indicate basically that different time‐dependent formations of two structural units dominate the mechanical properties: (i) A fast formation of longer (polymeric) silicate chains is enforced by the consumption of hydroxide in the solution of metakaolin up to about 25 h of aging. (ii) An aluminosilicate network grows slowly and encloses the chain‐like units giving rise to an initial increase in strength within 100 h. During further aging the destruction of the polysilicate chains weakens the geopolymer. The destruction of the chain‐like units is explained by the increasing amount of hydroxide produced during network condensation. The results imply that the same reactions occur for aging at a higher temperature but on faster time scales.

Influence of the addition of grinding dust to a magnesium phosphate cement matrix

Magnesium phosphate cement materials were prepared by reacting magnesium oxide with water-soluble phosphates such as mono-ammonium dihydrogen phosphate (ADP), which solidified at ambient temperature through the formation of hydrated phases in the material. Cylindrical specimens of magnesium phosphate cement were molded and varying amounts (0–40% weight) of grinding dust, waste generated in the clutch disc finishing process by grinding and polishing, were added to the ceramic matrices. The influence of the addition of grinding dust on the characteristics of the cement compositions was verified in terms of setting time, apparent porosity, density and leaching/solubilization tests. The setting time was analyzed according to NM 65 (the Vicat needle) and by indirect calorimetric measurements, the apparent porosity and density of the materials were analyzed by the water immersion method, based on the Archimedes principle. Using an Instron 5500R universal testing machine, various analyses were made to ascertain how the different waste contents in the compositions affected the mechanical strength (axial compression and tensile strength by diametral compression). The results obtained proved highly satisfactory for the application of this waste as an additive in magnesium phosphate mortars. The addition of grinding dust to the magnesium phosphate cement matrix did not affect the formation of new phases or the setting time to any appreciable extent, but an increase in grinding dust content led to an initial increase in strength up to a given limit (about 30% of waste).

Progressive resistance training in neuromuscular patients. Effects on force and surface EMG

In a randomized clinical trial the efficacy of strength training was studied in patients with myotonic dystrophy ( n=33) and in patients with Charcot-Marie-Tooth disease ( n=29). Measurements were performed at the start and after 8, 16 and 24 weeks of progressive resistance training. Surface electromyography (SEMG) of proximal leg muscles was recorded during isometric knee extension at maximum voluntary contraction (MVC) and at 20, 40, 60 and 80% of MVC. Changes in MVC, maximum electrical activity and torque–EMG ratios (TER) were calculated. Fatigue was studied by determining the changes in endurance and in the decline of the median frequency ( F med) of the SEMG during a sustained contraction at 80% MVC. These parameters showed no significant changes after the training in either of the diagnostic groups. Only the Charcot-Marie-Tooth training group showed a gradual significant increase in mean MVC over the whole training period (21%). After 24 weeks, the increase in mean RMS was similar (25%), but this was mainly due to a sharp rise during the first 8 weeks of training (20%). The findings indicate that the initial strength increase was due to a neural factor, while the subsequent increase was mainly due to muscle hypertrophy.