Paper discusses the influence of the concrete mixture compaction time on density and compressive strength of hardened concrete samples. Concrete specimens, of diameter about 106 mm (D) and height about 1000 mm (H), were formed during the experiment. The ratio of height and diameter H/D was 9.4. Concrete mixture, placed in forms, was compacted by poker vibrator, when vibrating element was placed to the top part of the form. Different time was used for compacting mixture in forms: 0, 3, 6, 9 and 12 s. The study results show the changes in density and compressive strength of samples (radius about 106 mm and height about 100 mm) depending on the location of the sample in specimen (1000 mm height). It was found, that samples taken from different height of the specimen had different density and compressive strength.
Abstract.Recently the usage of various industry wastes as a secondary raw material tends to increase its relevancy. One of possible options to decrease the amount of waste is to use them to produce new products or materials. The operation of various secondary raw materials (tire rubber, tire cord, ground glass shards, ground ceramic waste products) during the concrete mixture preparation allows to change its as well as cured concrete properties. Recently polymer and steel fibers are used for concrete reinforcement. This study analyses the usage possibility of plastic shavings for the reinforcement of concrete. The technological properties of cement slurry (sand, fraction of 0/4 and 10 kg/m 3 , 15 kg/m 3 and 20 kg/m 3 of plastic shavings) as well as mechanical, physical and porosity properties of cured sandcrete were established during the experimental research. The geometric characteristics of mill-shredded plastic shavings were established. Experimental results revealed that the usage of plastic shavings decreased slurry slump and density. The minor decrease of cured sandcrete density (~2200 kg/m 3 ) was noticed with the addition of plastic shavings within the limits of 10 -20 kg/m 3 . The flexural strength of cured sandcrete increased from 36 % to 57 % compared with reference specimen (without plastic shavings). The dependence of flexural force and deflection was obtained. Study revealed that the residual strength after crack opening is bigger with the usage of plastic shavings as a secondary raw material compared with reference specimen.
Santrauka. Tyrimo metu nustatyta kompleksiné bei atskini skirtingos paskirties cheminiii pdedii itaka cementinio akmens podngumo rodikliams -atvirajam ir uzdarajam podngumui, vidutinio poni dydzio ir poni vienodumo rodikliams. Tydmuose naudoti cheminiai pdedai: plastifikuojantis, klampei modifikuojantis ir mi §inyje susiformavusias oro poras suardantis pdedas. Nustatyta, kad cemento tesloje (V/C -0,45) esant pastoviam plastifikuojancio pdedo kiekiui -1,0 % cemento mases, klampm odifikuojancio pdedo kiekiui kintant nuo 0,1 iki 0,6 %, o misinyje susiformavusias oro poras suardancio pdedo kiekiui kintant nuo 0,05 iki 0,3 %, cementinio akmens atvirasis podngumas svyruoja nuo 30,21 iki 31,06 %, o uz:darasis -nuo 5,39 iki 6,22 %. Cemento tesloje virsijus plastifikuojanöio pdedo 1,1 % cemento mases, cementinio akmens atvirasis podngumas padidéja apie 1,4 karto, o uzdarasis podngumas sumazéja apie 2,5 karto. Pddéjus lte §1^0,l % cemento mases klamp^ modifikuojanöio pdedo, cementinio akmens atvirasis podngumas padidéja apie 1,5 karto, uzdarasis podngumas sumazéja apie 2,4 karto. Oro poras suardancio pdedo kiekis 0,05 % cemento mases cementinio akmens atvir^i podngum^ padidina apie 1,5 karto, uzdar^i podngum^ sumazina apie 3,5 karto.ReikSminiai zodziai: portlandcementis, cheminis pdedas, plastifikuojantis pdedas, klamp^ modifikuojantis pdedas, susiformavusias oro poras miSinyje suardantis pdedas, cementinis akmuo, vandens igéds, podngumas. AbstractThe conducted research has established a complex influence and the impact of separate chemical admixtures of different purpose on the parameters of the porosity of hardened cement paste such as open and closed porosity, the average size of pores and the rates of pore inequality. According to the parameters of the porosity of hardened cement paste, on the basis of A. E. Sheikin's methodology, the number of freezing-thawing cycles was predicted. This research used plasticizing, viscosity modify-535
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