دانلود رایگان مقاله انگلیسی تأثیر اسکوریا بر برخی ویژگی های مختلف بتن سبک - اشپرینگر 2017

Abstract:

Experimental research on the technical characteristics of lightweight concretes incorporating scoria was conducted. The objective of this research is to investigate the feasibility and effectiveness of the use of scoria, in lightweight concretes. Coarse scoria of 5/10 and 10/20 mm were used. A portion of the aggregate mixtures had an average particle size B100 lm. Scorias are often used as the constituents of structural concrete and insulating materials. The usability of the concretes tested in this study broadens as the porosity of the mixtures decreased and the cement dosage increased. According to the cement dosage and frequency types, the absorption coefficients of concretes ranged from 0.14 to 0.47. A compressive strength of 19 MPa corresponded to a density of 1800 kg/m3 ; compressive strengths from 10 to 18 MPa mapped to densities ranging from 1300 to 1700 kg/ m3 . The thermal conductivity of mixed concretes without scoria reached a maximum value of 0.268 W/m K. The thermal conductivity values of the concretes mixed without sand were below 0.403 W/m K. As sand content increased, the conductivity evolved from 0.565 to 0.657 W/m K. Freeze–thaw stability tests were conducted for 400 cycles or until specimens deteriorated. The experimental results helped in determining the optimum mixing conditions for the inclusion of scoria in cement to produce lightweight concretes.

4. Conclusion

Based on the average compressive strength after 28-day aging, thermal conductivity, acoustical absorption coeffi- cient, expansion (stretch) after 300 freeze–thaw cycles without salts, and the scaling cumulated mass after 56 freeze–thaw cycles with salts, the following conclusions can be drawn for the studied materials and proportions: - Low-resistance scoria concretes can be used in the domain of thermo–acoustical insulation; - Ternary concretes placed behind binary concretes provide improvements in sound absorption on the order of 75% at low and intermediate frequencies. Thus, they can be used to weaken noise from a room to another or on both sides of a wall;

- By changing the average size of the large aggregate from 5 cm to 10 cm, the scoria concrete strength increases to 8% after 40 freeze–thaw cycles;

- The susceptibility to salt scaling of scoria concrete is not correlated with the susceptibility to internal frost action.

- Coarse scoria were used in two concrete samples of the same density of 450 kg/m3 . The average strength at 28 days was 14 MPa for the sample containing natural aggregates and 16.9 MPa for the soaked aggregates that had previously been mixed with water for 30 min. This represents a relative increase of approximately 20% over the strength of the reference concrete.