Dielectric Relaxation and Alternating-Current Conductivity of Highly Crystalline Poly (ethylene-2,6-naphthalenedicarboxylate) Films

Journal of Electronic Materials - The dielectric relaxation and alternating-current (AC) conductivity behavior of poly(ethylene-2,6-naphthalenedicarboxylate) are found to be sensitive to its degree...     

Properties of self-compacting mortar made with various types of sand

Higher cement and fines content is needed in self-compacting mortars (SCMs) to increase their flowability and stability. Different inert fillers and supplementary cementitious materials are usually added. The use of sands rich in fines may be a cost effective alternative source of filler. This paper presents the results of an experimental study on the rheological and mechanical properties of self-compacting mortars (SCMs) made with various types of sands: crushed sand (CS), river sand (RS), dune sand (DS) and a mixture of different sands. The mini-slump flow, V-funnel flow time and viscosity measurement tests were used to study the rheological properties. The experimental results indicate that the rheological properties and strength improve with mixtures of crushed and river sands but decrease with mixtures of crushed and dune sands especially for higher dune sand content. Crushed sand with (10–15%) of limestone fines can be used successfully in production of SCM with good rheological and strength properties. However, a reduction in compressive strength with increasing dune sand content (up to 50%) in mortar with binary and ternary sands was observed.     

Effects of experimental ternary cements on fresh and hardened properties of self-compacting concretes

Self-compacting concrete (SCC) is a concrete that flows alone under its dead weight and consolidates itself without any additional compaction and without segregation. As an integral part of a SCC, self-compacting mortars (SCMs) may serve as a basis for the mix design of concrete since the measurement of the rheological and viscosity properties of SCC is often impractical due to the need for complex equipment. This paper discusses the properties of SCM and SCC with mineral additions. ordinary Portland cement (OPC), natural pozzolana (PZ), and marble powder (MP) are used in ternary cementitious blends system following the cement substitution with PZ and MP in ratio 1/3. Within the framework of this experimental study, a total of 12 SCM and 6 SCC were prepared having a constant w/b ratio of 0.40. The fresh properties of the SCM were tested for mini-slump flow diameter, mini-V-funnel flow time, and viscosity measurement. Slumps flow test, L-box, J-ring, V-funnel flow time, and sieve stability were measured for SCC. Moreover, the development in the compressive strength was determined at 3, 7, 28, 56, and 90 days. Test results have shown that using ternary blends improved the fresh properties of the mixtures. The combination of natural pozzolana and marble powder increase the slump flow test up to 826 mm for the mixture prepared with 10% of mineral additions. Moreover, the use of mineral addition reduced the time flow to 4.27 s for SCC with 20% mineral addition, thus reducing the viscosity of all mixtures. Addition of MP increases the capacity of the passage through the plates between 88.75 and 93.50% for SCC with 7.5 and 15% of MP, respectively. The ternary system (PZ and MP) improve the sieve stability with the value for 4.07% of SCC with 50% of substitution compared for SSC without additions. The compressive strength of SCC at 90 days with 40% of PZ and MP was similar to that of OPC.     

Effect of fine aggregate replacement with desert dune sand on fresh properties and strength of self-compacting mortars

This paper presents the results of an experimental study that investigated the rheological and mechanical properties of self-compacting mortars incorporating fine dune sand (DS), which has a tight Particle size distribution. Mortar mixtures were prepared with crushed sand (CS) or river sand (RS) in which the fine aggregates were replaced partially by different percentages of DS of 0, 25, 50, 75 and 100%. The effect of DS on the fresh mortars properties was studied using the mini-slump flow, V-funnel flow time and viscosity measurements tests. Compressive strength and flexural strength were determined at age of 3, 7 and 28 days. Experimental results indicate an improvement in fresh rheological without reducing in mechanical properties of self-compacting mortars when fine aggregates were replaced partially with DS (50%). However, at high-level DS replacement (75%) the slump flow decreases. The replacement of the DS to the CS or to the RS shows an increase in the mixture viscosity. In general, the compressive and flexural strength were not significant affected with an increase in DS replacement. Finally, based on the results obtained in this investigation, DS may provide a readily available alternative material as fine aggregates in mortar application.     

Rheology of ordinary and low-impact environmental concretes

This study deals with the rheological properties of concrete mixtures incorporating various types of mineral additions as a partial replacement of cement in order to produce a low-impact environmental concrete. The control mixture contained only Portland cement as the binder, while the remaining mixtures incorporated binary cementitious blends of slag, limestone filler, and fly ash with different rates of replacement. After mixing, the plastic viscosity and yield stress of the concretes were evaluated at different slump values using a rheometer apparatus. The results showed that the type of mineral additions and the rate of substitution affect the rheological parameters of low-impact environmental concrete. Indeed, increasing the degree of substitution leads to an increase in the plastic viscosity of the concrete made with different types of additions used in this study.     

Physical and mechanical properties of concrete repair materials in dry and hot-dry environment

A variety of repair materials is available in the market. It is often difficult to select a suitable repair material for a given condition. Various researchers use different evaluation methods, but the required specifications are not established. The main objective of this work is to study the physical and mechanical properties of ready-mixed repair mortars available in the Algerian local market. The experimental study was carried out on three types of repair mortars: cement-based mortars, with and without fibers. The properties of the repair mortars at hardened state are analyzed for compressive, flexural and bond strengths, capillary water absorption, and shrinkage. The effect of humid curing using Hessian regularly humidified, on the compressive strength in hot and dry environment was also studied. The results of the experimental study showed that the repair mortar containing silica fume and synthetic fibers gave a better strength in all curing environments. The study showed also the negative effect of hot and dry environment on all types of ready-mixed repair mortars, and demonstrated the importance of humid curing during early age.