Influence Of Curing Systems Research Articles

Influence of curing system on static and dynamic mechanical properties of fly ash concrete

This paper investigates the effect of curing conditions on the static mechanical properties of fly ash concrete such as compressive strength and stress–strain behavior, and utilizes the split Hopkinson pressure bar (SHPB) device to characterize the dynamic mechanical responses of steam-cured concrete under different strain rates. Experimental results reveal that the strength of static concrete decreases with the increase of fly ash (FA) content and increases first and then decreases with the increase of steam curing temperature. The substitution of fly ash for cement reduces water consumption, weakens the hydration degree of cement, and affects the development of static concrete strength. The steam curing temperature plays a role in promoting cement hydration within a certain range, but high temperature leads to the destruction of concrete microstructure, thus inhibiting the development of strength and leading to the instability of concrete performance. The steam curing temperature effects on the dynamic compressive strength of concrete is receded with the increase of strain rate. When the steam curing temperature is constant, the dynamic compressive strength of concrete increases gradually with the increase of strain rate, and the influence of strain rate on the dynamic compressive strength of concrete is greater than that of steam curing temperature. The analysis of the scanning electron microscope (SEM) confirmed that the decrease of concrete strength was due to the change of temperature and fly ash content, which increased microstructure pores, thus affecting the development of strength. This study has important guiding significance to improve the safety of engineering facilities and adapt to the development of modern engineering towards heavy load, long span, and harsh environment.

Influence of wetting-drying curing system on the performance of fiber reinforced metakaolin-based geopolymer composites

In this study, mechanical and durability properties of geopolymer composites prepared using metakaolin and colemanite binding materials with basalt and polyvinyl alcohol fibers were investigated under the influence of curing systems. For the 7 series prepared, two different curing conditions have been applied: wetting-drying and heat curing. The mechanical properties of geopolymer samples were investigated for 7 and 28 days strength and ultrasonic pulse velocity results, water absorption, unit weight and porosity. After the abrasion test, weight loss and length change were examined and after the high temperature tests of 200, 400 and 600 °C, the results of strength, ultrasonic pulse velocity and weight loss were found. The results showed that the residual strength values were high after high temperature tests. As a result of SEM, FT-IR and TGA-DTA analyzes, it was observed that high temperature post-geopolymer samples retained their stable structure. When the wetting-drying curing was applied, it was observed that the SiOAl bonds were higher in the FT-IR results. This showed a higher rate of geopolymerization and increased strength values. Similar behaviors were observed according to TGA-DTA results, and weight loss with temperature was found to be lower in samples applied to wetting-drying curing. Also, there was a positive effect on the strength results with the increase in basalt and polyvinyl alcohol fibers ratio. The main reason for this situation is the formation of a resistant layer with the effect of basalt and polyvinyl alcohol fibers. The compact structure of the geopolymeric matrix brings along a good degree of adhesion. This allows geopolymer samples to resist freezing-thawing. In geopolymer samples, despite the 90 cycles, the residual strength were high and the decrease in the ultrasonic pulse velocity rate results were limited.

Structure–properties of electron beam irradiated and dicumyl peroxide cured low density polyethylene blends

AbstractLow density polyethylene (LDPE) and its blends with styrene butadiene rubber and ethylene propylene diene monomer were cured, using electron beam irradiation as well as dicumyl peroxide (DCP). The effect of blending was found to change the melt viscosity when compared with the virgin LDPE. Also, the influence of curing system on the various properties was investigated. It was found that either irradiation or DCP curing enhanced the gel content and crosslink density as well as the mechanical and hot set properties. The obtained data showed that the curing greatly influence the stress strain and hot set properties, in which there is a variation in such properties for both curing methods in spite of the gel contents were comparable. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Influence of internal strain on change of crosslink density of natural rubber vulcanizates by thermal ageing

Change of crosslink density of natural rubber (NR) vulcanizates by thermal ageing at 60 °C has been studied under swollen conditions in solvents to investigate the influence of internal strain applied to the vulcanizate on the crosslink density change. The internal strain was controlled by swelling with various solvents such as n-hexane, toluene, tetrahydrofuran (THF), methanol and water. The order of degree of the swelling is toluene ≈ THF > n-hexane > methanol > water. The influence of curing system has been investigated with the vulcanizates cured by the conventional and EV cure systems. After thermal ageing, the apparent crosslink densities of the swollen vulcanizates in n-hexane, toluene and THF decrease irrespective of the cure systems, while that of the swollen vulcanizate in water increases. For the swollen vulcanizates in methanol, the apparent crosslink density of the vulcanizate with the conventional cure system after thermal ageing increases while that of the vulcanizate with the EV cure system decreases. The decrement of the apparent crosslink density of the vulcanizate after thermal ageing becomes larger and larger upon increasing the internal strain. © 2001 Society of Chemical Industry

Effect of curing systems and temperatures on the activity of retarder in natural rubber mixes

The effect of vulcanization temperature (150° and 180°C) on the structure and technical properties of gum natural rubber vulcanizates with four different 2-(morpholinodithio)-benzothiazole (MDB) — sulphur ratios in presence of N-(cyclohexyl thio)-phthalimide (CTP, 0.5 phr) has been determined at the respective optimum cure times. The influence of curing system, temperature and retarder on (a) the chemical crosslink density, (b) the distribution of crosslink types, (c) the extent of sulphidic main chain modification and (d) the zinc sulphidic formation have been investigated. The network results have been correlated with the technical properties. Increasing the cure temperature by 30°C (from 150° to 180°C) does not alter the activity of CTP. It is effective in all curing systems, but effectiveness was maximum in the conventional system. At 0.5 phr level, CTP caused reduction in most technical properties.

The influence of curing systems on the properties of natural rubber

AbstractAfter a brief historical introduction the influence of curatives on the chemical structure of vulcanizates is discussed. Emphasis is given to physically important features of network structure such as crosslink density, crosslink type, and various main‐chain modifications. The significance of extra‐network materials such as curative residues and zinc soaps is introduced. Nonsulfur systems are briefly considered.The effects of differences in network structure and in extra‐network materials on aging properties is outlined with special emphasis on the importance of total combined sulfur, conjugated triene groups, and curative residues. The special problem of finding suitable antioxidants and antiozonants for peroxide cured rubber is mentioned. The influence of different curing systems on the crystallization of natural rubber both at low temperatures and at large extensions is described and shown to be a similar function of vulcanizate structure in both cases when compared at constant degrees of crosslinking. Problems in the interpretation of stress‐strain behavior are reviewed.Changes in the C1 term of the Mooney‐Rivlin relation can only be interpreted as changes in crosslink density or as a filler stiffening effect of insoluble extra‐network material. Changes in the C2 term of this relation also take place as the curing system is changed and are correlated with inelastic behavior. Analysis of stress‐strain relations at high strain using the Martin‐Roth‐Stiehler equation indicates significant differences in the strain‐induced crystallization behavior of vulcanizates based on various curing systems, even when compared at similar crosslink densities.The inelastic stress‐strain properties of natural rubber vulcanizates are divided into three main regions: (a) the glass transition region; (b) the chemical transition region, and (c) the intermediate region. The effects of network structure and extra‐network materials in each region are considered separately. In particular, the effects of zinc soap structurization on stress relaxation behavior in the intermediate region is described, including the likely mechanisms by which rubber‐soluble zinc soaps reduce the stress relaxation rate.The influence of curing systems on the strength properties of homogeneous and isotropic natural rubber vulcanizates is described briefly, with particular emphasis on the role of polysulfidic crosslinks and main‐chain modifications.