International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

In recent years, the use of internal crystallization chemical admixtures for concrete and mortar to increase their water-tightness and other physical and mechanical characteristics has been of increasing importance in modern construction. These types of chemical modifiers allow for the effective replacement of conventionally performed waterproofing works (membranes, rolls, brushed or sprayed coatings, etc.) by purposefully improving the physical-mechanical characteristics of structural concretes, rendering them, to one degree or another, impermeable to water or/and aggressive agents from different origins. In the specialized world market for such products there are several leading competing companies – producers of internal-crystallization chemical admixtures, which have different activity in Bulgaria. The new extended research on such several new types of those admixtures were reported and discussed. The complex mechanical and structural tests are conducted and respective results are compared to predict the admixture’s efficiency of their ability to limit the ingress of water into concrete and reinforced concrete sections, as well as their ability to increase the durability of concrete as the main structural material.

The technical design of ETEM factory (Sofia) requires the specialized conveyor stretching machine to be monolithic fitted by using of system of steel anchor rods with a diameter of 30 and 40 mm and different lengths (600-700 mm), which have to be grouted in pre-left holes with a diameter of about 150 mm in steel-reinforced concrete foundation slab.
The technically determined anchoring depth determines the total thickness of the anchor layer within 700-800 mm, reaching the “lower edge of the steel support plate”. The company’s produced grouting compositions generally have significant limitations in terms of the maximum allowable thickness of a single layer – usually up to 30-40 mm, which implies multi-stroke implementation to fill the entire anchoring depth.
Given the above, and mainly, taking into account the conditions of laying and the specifics of the operating mode of the facility, thepossibility to use concrete batching plant produced high-strength self-compacting fiber-reinforced concrete with compensated shrinkage (to some degree of self-stressing) is estimated as an attractive alternative from a technical and financial point of view.
After the innovative mix design of that an innovative composition of concrete and its casting in real production conditions, specialized laboratory tests were conducted to prove its strength-deformation characteristics – compressive strength, tensile strength in bending, modulus of elastic deformation and shrinkage characteristics. The obtained results prove that the required high technical and technological characteristics of the concrete mix and the hardened concrete are completely achieved precise for the specific application ca se.

Solvay Sodi JSC, Devnya, Bulgaria, is the biggest calcinated soda production plant in Europe. It is built in 1974 and it works in three-shift production regime up to present days. The exploitation environment is highly influenced by numerous factors, act ing corrosively on main reinforced concrete structures – active atmospheric processes (in continental type moderate climate), sea water born chlorideaerosols, as well chemical attack caused by carbon dioxide and nitric acid, presented in the air in form of evaporation. The most reinforced concrete structures need urgent remedial measures to restore the load-bearing capacity of its components.
The “light soda” silos are reinforced concrete facilities (cylindrical shells) which repair has to be executed dur ing continuous production process. The options for repair of these structures and restoration of their load bearing ability by specially designed innovative high-tech hybrid reinforced sprayed concrete, containing capillary crystalline admixture, are discussed in the report.
It is well known that two basic methods of shotcrete exist – “dry” and “wet” ones.
The report discusses the main advantages of the specially designed innovative hybrid fiber-reinforced “wet” shotcrete for thin repairing overlays, compared to industrially made “dry” one. By purposeful using of standard and direct physical test methods the basic long -term mechanical and structural characteristics of two composites are presented and discussed. The effectiveness of the proposed “wet” method is based to real possibilities to involve in concrete mix design different chemical innovative admixtures – ultra high range water reducing (HRWRA), shrinkage compensating (ShCA), internal crystallization one, etc. The mechanical properties of “wet” one dramatically exceeded respective ones of the “dry” one. The mechanical test results fully correspond to the respective long -term structural characteristics, obtained by using of X-Ray, DTA, SEM and BET-methods.
It could be concluded that the innovative hybrid fiber-reinforced “wet” shotcrete is preferable for high-performance thin repairing overlays
for structural strengthening of damaged concrete structures.

In recent years, the use of internal crystallization chemical admixtures for concrete and mortar to increase their water-tightness and other physical and mechanical characteristics has been of increasing importance in modern construction. These types of chemical modifiers allow for the effective replacement of conventionally performed waterproofing works (membranes, rolls, brushed or sprayed coatings, etc.) by purposefully improving the physical-mechanical characteristics of structural concretes, rendering them, to one degree or another, impermeable to water or/and aggressive agents from different origins. In the specialized world market for such products there are several leading competing companies – producers of internal-crystallization chemical admixtures, which have different activity in Bulgaria. Based on results of purposeful set of structural investigations (DTA, SEM, BET) conducted the purpose of the report is to assist participants  in the construction investment process in understanding the nature, specific characteristics and differences in the performance (effectiveness) of different products in terms of their ability to limit the ingress of water into concrete and reinforced concrete sections, as well as their ability to increase the durability of concrete as the main structural material.

The paper proposes a complex assessment of the post-fire state of steel reinforced concrete structures. It covers a combined usage of mechanical tests (core cutting and testing), non-destructive assessment of concrete strength, indirect physical (ultrasonic) methods and direct physical methods (X-ray structural and differential- thermal analyses). The complex analysis of the results enables one to assess the state of the structure and outline means of its strengthening, thus guaranteeing further flawless operation..