No abstract

A comparison of the effect of steel and polypropylene fibers on the strength, frost resistance, abrasion, and corrosion resistance in an acidic environment of fiber-reinforced concrete for industrial floors and road pavements was carried out. Steel fibers with a length of 50 mm and a diameter of 1 mm and polypropylene fibers with a length of 36 mm and a diameter of 0.68 mm were used. The amount of steel fiber varied from 15 to 25 kg/m3, and the amount of polypropylene fiber varied from 2 to 3 kg/m3. It has been established that steel fiber more significantly increases the concrete compressive strength, and both types of dispersed reinforcement increase the flexural strength equally by 27–34%. Also, dispersed reinforcement reduces the concrete abrasion resistance by 15–35% and increases its frost resistance by 50 cycles, which helps to improve the durability of industrial floors and road pavements. The use of steel fiber in an amount of 20 kg/m3 and polypropylene fiber in an amount of 2.5 kg/m3 also increases the concrete corrosion resistance in an acidic environment. In general, dispersed reinforcement with both fiber types has approximately the same technological effect concerning the mentioned applications. However, the use of polypropylene fibers is economically more profitable since an increase in the cost of 1 m3 of concrete with steel fiber reinforcement is from $22.5 to $37.5, and an increase in cost with polypropylene fiber is from $10 to $15.

Any damage to the column and in particular the reducing of the cross section, requires steps to repair the columns, taking temporary measures in the form of taking part of the load and / or reducing the useful load on the damaged column. In order for these measures to be applied more adequately and at the same time preventing adverse effects, it is necessary to define the actual impact of certain cross-sectional damage on the bearing capacity. In this paper the conceptual, mathematical and system dynamics models of the effect of the force on damaged reinforced-concrete column were developed, according to the real values of the failure force. The prediction model is adaptable and it can also be used for the other length slender, the other angle of damage or the depth of damage. The methods of modelling and conceptualization of such situations contribute significantly to protection of architectural heritage. In addition, the economic component of the system should also be taken into consideration. The developed adaptive model allows setting the optimal parameters of the model according to the needs.

The influence of the hardening accelerator and steel fiber on the concrete adhesion strength for the repair of rigid highway and airfield pavements has been investigated. The concretes were mixed based on the CEM II/A-S 42.5 and included MasterGlenium SKY 608 superplasticizer. Experiment with two variable concrete composition factors was carried out. The amount of steel fiber varied from 0 to 100 kg/m3, the amount of Sika Rapid hardening accelerator varied from 0 to 9.6 kg/m3. It was found that modified repair concretes have a sufficiently high adhesion strength to "old" concrete, from 2.30 MPa when tested by the pull-off method and from 2.05 MPa when tested by the flexural strength test method. Fiber-reinforcement increases the adhesion strength of repair concrete by 7-15% due to reducing of shrinkage during hardening. Treating the contact surface of "old" concrete with a primer additionally increases adhesion strength by 6-10%. The maximum adhesion strength of fiber-reinforced concrete to the base reaches 3 MPa. Due to the high early and design strength, modified steel fiber-reinforced concrete provides the possibility of quick resumption of traffic while ensuring the integrity of the road structure due to the joint work of the repair material with the old concrete repair area.

High-early strength fiber-reinforced concretes are effective materials for the full depth repair of rigid highway and airfield pavements. A comprehensive study was carried out on the influence of the amount of steel anchor fiber and hardening accelerator on properties that are important for repairing concrete. A two-factor experiment was carried out, in which the influence of the hardening accelerator and fiber dosages on the strength, frost resistance, wear resistance and shrinkage of repaired steel-fiber-reinforced concrete for rigid pavements was studied. The investigated concretes contained 400 kg/m3 of cement and polycarboxylate plasticizer in the amount of 1.2% of the cement content. It has been established that the optimal concrete compositions are with the amount of Sika Rapid 3 hardening accelerator from 1 to 2% of the cement content and the steel fiber amount from 60 to 90 kg/m3. Optimal fiber-reinforced concrete compositions have a reduced shrinkage during hardening, and at the age of 2 days they have a compressive strength of at least 55 MPa and a flexural strength of at least 8.5 MPa. At the design age, the fiber-reinforced concrete compressive strength is 85–90 MPa, its flexural strength ranges from 15.5 to 17.5 MPa, it has a frost resistance of F200 and abrasion not higher than 0.24 g/cm2. These properties ensure the high durability of the repair material.