This article describes the observed and examined effect of crumb rubber on the strength (compressive, bending and splitting tensile) of concrete. The tests have shown that the change in the strength of concrete with crumb rubber waste additives can be forecasted from exponential equations. These relationships enable to foresee the regularities of strength properties when a certain amount of crumb rubber of a certain size fraction is added to concrete. The obtained exponential equations show that concrete compressive, flexural and splitting tensile strengths decrease with increasing crumbed rubber additive amount. The testing has also shown that the addition of a small amount of crumbed rubber slightly increases (7%) the tensile splitting strength. The reason is better adhesion of the cement stone with rubber particles compared to the adhesion of sand, which was replaced by crumbed rubber. With higher content of crumbed rubber additive in the concrete, the tensile splitting strength decreases due to the significant increase of entrained air content and lower density.

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This paper analyzes concrete fine aggregate (sand) modification by scrap tire rubber particles-fine crumb rubber (FCR) and coarse crumb rubber (CCR) of fraction 0/1mm. Such rubberized concrete to get better bonding properties were modified by car-boxylated styrene butadiene rubber (SBR) latex and to gain the strength were modified by glass waste. The following tests—slump test, fresh concrete density, fresh concrete air content, compressive strength, flexural strength, fracture energy, freezing-thawing, porosity parameter, and scanning electron microscope—were conducted for rubberized concretes. From experiments, we can see that fresh concrete properties decreased when crumb rubber content has increased. Mostly it is related to crumb rubber (CR) lower specific gravity nature and higher fineness compared with changed fine aggregate-sand. In this research, we obtained a slight loss of compressive strength when CR was used in concrete However, these rubberized concretes with a small amount of rubber provided sufficient compressive strength results (greater than 50 MPa). Due to the pozzolanic reaction, we see that compressive strength results after 56 days in glass powder modified samples increased by 11–13% than 28 days com-pressive strengths, while at the same period control samples increased its compressive strength about 2.5%. Experiments have shown that the flexural strength of rubberized concrete with small amounts of CR increased by 3.4–15.8% compared to control mix, due the fact that rubber is an elastic material and it will absorb high energy and perform positive bending toughness. The test results indicated that CR can intercept the tensile stress in concrete and make the deformation more plastic. Fracturing of such conglomerate concrete is not brittle, there is no abrupt post-peak load drop and gradually continues after the maximum load is exceeded. Such concrete requires much higher fracture energy. It was obtained that FCR particles (lower than A300) will entrap more micropores content than coarse rubbers because due to their high specific area. Freezing-thawing results have confirmed that Kf values can be conveniently used to predict freeze-thaw resistance and durability of concrete. The test has shown that modification of concrete with 10 kg fine rubber waste will lead to similar mechanical and durability properties of concrete as was obtained in control concrete with 2 kg of prefabricated air bubbles.

Every year, colossal amounts of used and non-biodegradable rubber tyres are accumulated in the world. Experience shows that the most efficient way to increase the concrete fracture energy G F (N/m) is to use metal or polypropylene fibres. The optimal content of fibre increases concrete resistance to stress (especially tensile stress under bending force). Concrete fracture is not brittle; concrete continues deforming after maximum stresses and is able to resist certain stresses, there is no abrupt decrease in loading. The research has proved that crumb rubber can be used in concretes as an alternative to metal and polypropylene fibres. The investigation has found that rubber waste additives, through their specific properties can partly take up tensile stresses in concrete and make the concrete fracture more plastic; besides, such concrete requires a significantly higher fracture energy and concrete samples can withstand much higher residual strength at 500 mm crack mouth opening displacement (CMOD) and deflection.

This paper analyses the effect of mineral additives on alkali-silica reaction. Amorphous SiO 2 contained in concrete aggregate is known for reactions with Na 2 O and K 2 O that cause concrete expansion and cracking. Concrete expansion is the result of silicates reaction (ASR). Alkali silica gel is a reaction product having expanding properties. Expanding silica gel creates stress that causes concrete cracking. The paper investigates the elimination of the negative effect of ASR by using fly ash as active mineral additive. In the tests active mineral additive (fly ash) is expected to reduce the effect of alkali-silica reaction and volumetric strain.

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The article focuses on investigation of mechanical and fracture properties of concrete containing electrical cable waste as well as some microstructural features of such concrete. Added to concrete, electrical cable waste reduces the overall concrete bulk density. compressive, flexural, tensile splitting strengths and elastic modulus decreased when electrical cable waste was admixed to conventional and polymer modified concretes. the best mechanical properties of concrete samples containing electrical cable waste were identified in polymer modified concrete containing 5% of electrical cable waste. electrical cable waste particles increase the deformability of polymer modified concretes and have almost no influence on normal concrete. consequently, the optimal amount of electrical cable waste particles can provide concrete with desirable strength that is required for different applications. Research interests: synthesis of crystalline and amorphous zeolites, zeolite modification and their sorption properties, use of zeolite in cement and concrete systems, special-purpose cement systems and concretes. Algirdas AUGONIS. Doctor of Technological Sciences, Lecturer at the Department of Building Materials of Kaunas University of Technology. Research interests: concrete fracture mechanics, fibre reinforced concrete, concrete deformability and strength. Henrikas SIVILEVIČIUS. Dr Habil. Prof. of the Department of Transport Technological Equipment of Vilnius Gediminas Technical University. Doctor (1984), Doctor Habil. (2003). Publications: more than 190 scientific papers. Research interests: flexible pavement life cycle, hot mix asphalt mixture production technology, application of statistical and quality control methods, recycling asphalt pavement technologies and design, decision-making and expert systems theory. Rėda BISTRICKAITĖ. Dr, Lecturer, at the Department of Building Structures of Kaunas University of Technology. Research interests: research of concrete and reinforced concrete innovative structures, mechanics of layered structures, new composite materials.

Santrauka. Nagrinėjama betono su elastingu priedu iš mechaniškai smulkintų naudotų padangų gumos atliekų priedo įtaka ciklinių apkrovų poveikiui. skirtingos frakcijos ir skirtingas gumos atliekų priedo kiekis buvo naudojamas betonuose. atlikti eksperimentai parodė, kad gumos atliekų priedas turi įtakos ciklinių apkrovų poveikiui. Gauta, kad to paties gniuždomojo stiprio betonuose su mechaniškai smulkintomis gumos atliekomis deformacijos po 20 ciklų 56-63 % didesnės, o liekamosios deformacijos nukrovus yra 219-360 % didesnės nei bandiniuose, kuriuose nebuvo naudojamas gumos atliekų priedas. Pastebėta, kad po ciklinių apkrovų poveikio bandiniai, kuriuose buvo naudojamos gumos atliekos, kur kas labiau deformavosi, susidarė daug didesnės ribinės deformacijos nei bandiniuose, kuriuose nebuvo naudojamas dempferuojantis gumos atliekų priedas. iš atliktų eksperimentų matyti, kad gumos atliekas tikslinga naudoti betono konstrukcijose, veikiamose daugkartinėmis nuolat pasikartojančiomis apkrovomis. Reikšminiai žodžiai: betonas, gumos atliekų priedas, ciklinės apkrovos, liekamosios deformacijos, ribinės deformacijos Downloaded by [University of Tennessee, Knoxville] at 09:26 22 December 2014 Statybinės konstrukcijos ir technologijos, 2009, 1(4): 172-182