This paper investigates ultimate strength of lightweight concrete specimens: cubes, cylinders, and prisms wrapped by different layers CFRP respect to several curing periods. The specimens were prepared and tested under compressive and flexural loading at the ages of 7 days and 28 days with varying confinement levels (from unconfined; 0L to double-layer of CFRP, i.e., 2L). The results showed that all three factors: confinement level, specimen geometry and curing age had a significant effect on both compressive strength as well as flexural strength. Indigenous soft soil was wrapped with various CFRP wraps to study the change in failure mode from brittle to ductile with an increase in confinement and two-layer WR-CFRPs exhibited the maximum gains in compressive and flexure-up to 48% compressive, 380% of flexural strength when compared with unconfined specimens. Cylindrical samples prove always more pronounced strengthening effect than cubes, probably because of having a more even stress field and less influence to the corner effects. Besides, the confinement effect became more significant when specimens were left to cure for 28 days, highlighting initiation of concrete maturity requirement for best CFRP development. The findings indicated that early-age confinement (7-day, 2L) achieved strength equal or superior to shear-critical fully cured unconfined specimens, and confirmed the potential of CFRP in emergency repair and retrofitting. However, the ultimate strengths were the best when using both multi-layer CFRP confinement and full curing. These results highlight the synergistic relationship between geometry optimization, curing regimen and advanced fiber reinforcements in enhancing the structural response of lightweight concrete structure.
In General, original reactive powder concrete (RPC) consists of a superplasticized cement mixture with silica fumes, steel fiber and ground fine sand (150-600 ىm). The main purpose of the present work is to produce and study some mechanical properties of lightweight reactive powder concrete using a superplasticized cement mixture with high reactivity metakaolin (HRM) instead of silica fume, steel fiber (with different ratios ) with ground fine sand (150-600 ىm) and light weight material called (Perlite ) also with different ratios .This investigation was carried out using several tests, these tests were compressive strength, modulus of rupture, modulus of elasticity, density and absorption, and performed for specimens at ages of 3, 7, 28 days, respectively. The tests results were compared with a reference mix. The experimental results shows that , with different ages, (for constant Perlit ratio for 0% to 10% as additional cementtitious materials) addition of 1% steel fiber will improve about (8.3%-10% , 3.2%-11%and 0.25%- 8%) for compressive strength , modulus of rupture, and modulus of elasticity respectively, and increase density, absorption about (0.8%-1.8%,4.5%-8.2%) respectively. Also an increase of steel fiber ratio to 2% will improve about (16.5%-20.3%, 9.0%-17%, and 1.7%-11.5%) for compressive strength , modulus of rupture and modulus of elasticity respectively, and increase density, absorption about (1.7%-2.3% , 7.3%-8.3%) respectively. For same steel fiber ratio about 0% to 2%, increasing Perlite ratio to 2.5% will decrease about (17.3%-18.8%, 9.5%-15.5%, 4.4%-16.6%, and 4.98% - 6.9%) for compressive strength, modulus of rupture, modulus of elasticity and density respectively and increase absorption to about (55.5% - 66.5%). Increasing the ratio to 5% will also make a decrease of about (36%-36.77%, 33.7%-37%, 16.5%- 21.88%and 15.91%-19.74%) for compressive strength, modulus of rupture, modulus of elasticity and density respectively and increase absorption for about (106%- 110.5%) . Increasing the ratio to 10% will also decrease about (45.98%-47.2%, 46.5-54.2%, 30.6%- 35.57%and 19.4%-23.36%) for compressive strength, modulus of rupture, modulus of elasticity and density respectively and increase absorption about(183%- 192.6%). To produce structural lightweight concrete, the tests results show that the optimum steel fiber is 1% by volume and optimum Perlite ratio is 2.5% by weight of cement as additional materials.