Introduction. Recently, coarse-grained crushed stone and sand mixtures reinforced with mineral binders, mainly of low strength grades, have become widely popular during repair and construction work on the road network of Ukraine. As a binder in these mixtures, mineral binders are used in pure form, in most cases cements or slag Portland cements are used, in an amount of 2 % to 4 % of the mixture weight. This dosage is usually sufficient to ensure the normative values of strength and frost resistance required by current standards.
Problems. However, in addition to the advantages, these materials also have certain disadvantages, such as low frost resistance, which is characteristic of low strength grades. The easiest way to increase frost resistance is to increase the content of mineral binder in the mixture, but this subsequently negatively affects the crack resistance of the base layer of the road surface and the appearance of reflected temperature cracks in the road surface layer. Previously performed studies have established that one of the options for increasing strength and frost resistance is the introduction of fiber fibers into the composition of reinforced crushed stone-sand mixtures.
Purpose of the work. Production verification of the previously obtained results of the study of the influence of polypropylene fiber reinforcement of coarse-grained crushed stone-sand mixture reinforced with cement on a forced-action mixer, further laying and compaction of the resulting material in the base layer of the road surface.
Materials and methods. For the production of reinforced crushed stone-sand mixture reinforced with cement, crushed stone-sand mixture C7 produced by LLC «Kryvbas-shchebin» from granite raw materials was used. Slag Portland cement PC II/B-Sh 400 produced by LLC «Mineral powders and mixtures» was used as a binder in the amount of 3.5 % of the mass of the mineral part. To ensure high-quality compaction, the optimum moisture content of the mixture was ensured with a total water content of 8.0 % by weight of the stone material. For micro-reinforcement of the mixture, polypropylene reinforcing fiber with a length of 18 mm was used.
The results. After the samples reached the age of 28 days, the samples were tested. The results showed that the introduction of polypropylene fibers into the composition of a coarse-grained crushed stone-sand mixture reinforced with M20 cement under production conditions, allowed to increase the compressive strength of the material by 19 % and the indirect tensile strength by 90 % of the values of the indicators for the mixture without polypropylene fibers. Also, after 10 freeze-thaw cycles, the frost resistance of the mixture containing polypropylene fibers significantly increased. In the studied case, the frost resistance coefficient in compression increased by 24 %, and in indirect tension by 34 %.
Conclusions. The introduction of fiber reinforcement technology for coarse-grained crushed stone-sand mixtures reinforced with cement of strength grade M20 increases all physical and mechanical indicators. Compressive strength increased by 19 %, and indirect tensile strength increased by 90 %. This also allowed to increase the frost resistance of the crushed stone-sand mixture reinforced with cement when testing samples in compression by 24 %, and in indirect tension by 34 %. Observation of the process of laying fiber-reinforced crushed stone-sand mixtures reinforced with cement using an asphalt paver and their compaction revealed no additional difficulties or difficulties. However, for a wider industrial application of this technology, there is a need to develop an additional fiber dosing system, synchronize it with the on-board equipment of the installation, and further include it in the overall work cycle.
