Durability of Building Structures and Constructions from Composite Materials

Russian Translations Series 109

V. Sh. Barbakadze, V.V. Kozlov, V.G. Mikul'skii, I.I. Nikolov

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000150438
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

This text deals with the estimation, prediction and improvement of the durability of building structures and constructions from composite materials with inorganic, organic and mixed binders. It describes a method for improving the durability of structures and constructions.

Section II

Glued Joints in Building Structures

4

Adhesives used in Building Structures

The problem of ensuring continuity of building structures is acquiring increasing significance because of the wider use of prefabricated reinforced concrete structures, notable volume of repairs and modifications of industrial buildings and increase in number of industrial units dealing with aggressive media. This problem may be solved by grouting the building structures with adhesive compounds having specific properties that provide overall strength, stability and durability to the structure while concomitantly reducing the inputs of labour, material and energy resources by eliminating electric welding and other ‘wet’ grouting processes.

Adhesive compounds are used for grouting reinforced concrete structures of industrial and public buildings and also hydrotechnical structures, bridge structures, elements of lining blocks of tunnels and chemically stable structures. They are also employed for repair and strengthening of a variety of structures.

The adhesive compounds used in building structures have all the features and structure typical of composite materials. Hence investigations were conducted to improve the matrix as well as the secondary phase in order to develop adhesive compounds that would meet the specific requirements of the structures to be grouted. Thermoreactive polymers, mineral binders and polymineral compositions were used as matrices for the adhesive compounds. Mineral fillers, thermoplastic polymeric fillers and oligomer processed mineral fillers, served as the secondary phase. A classification of the compounds investigated in this work.is given in Fig. 4.1 while that of the glued joints is given in Fig. 4.2.

4.1 Epoxy Adhesives

Epoxy adhesives have found wide application in various fields of engineering, including construction, because of their good adhesiveness to a large number of materials, small shrinkage, high cohesive strength and relatively low sensitivity to deviations from the prescribed gluing technology etc. [1, 2].

Fig. 4.1. Classification of adhesive compounds investigated.

Fig. 4.2. Classification of glued joints investigated.

While developing adhesive compounds, maximum attention is devoted to plasticising, cost reduction, enhancement of the stability of glued joints in aggressive media, improvement of crack resistance and reduction of the internal stresses.

In the proposed adhesive compounds, diane epoxide resins ED-16, ED-20 (GOST 10587–84) and alkyl resorcinol resin EIS-1 (Specifications TU-38-109-1-71) were used as binders. Epoxide polymers have good strength and stability but their excessive brittleness restricts their application. Given this fact, epoxide polymers are invariably plasticised. On the other hand, plasticising decreases the viscosity of epoxide’ polymers and intensifies the relaxation processes, thereby contributing to a reduction in the stresses inherent in glued joints.

The plasticiser is selected on the basis of the fundamentals of the theory of plasticising [39], taking into account the requirements of viscosity, strength and durability of the adhesive compounds and glued joints. In the epoxy resin-based adhesive compounds, the plasticisers used were ethers of polybasic acids (dibutyl phthalate, diactyl phthalate), oligomers (polyesters, furans), low molecular weight rubbers (polysulphides and butadiene acrylonitrites). The plasticising effect of ethers gradually wanes with time, yet dibutyl phthalate is widely used as a plasticiser because of its easy availability and ability to dilute viscous epoxy resins.

The best results are obtained by internal (structural) plasticising in which the plasticisers become chemically bonded to the oligomers. Examples of such plasticisers are rubbers, polyamides, polyester acrylates and other compounds that serve as hardeners to some extent. Plasticising of resins with elastomers results in inoculation of rubber molecules with the epoxide chains and consequent formation of transverse bridges that are more flexible than the bonds of polamines and other hardeners. Formation of copolymers of epoxide resin and rubber SKN-26 in the presence of amines is accompanied by separation of esters, followed by spatial cross-linking due to opening of the epoxide groups.

Interaction between thiokol and epoxide polymers occurs at the location of active hydrogen atoms of the mercaptan group. Plasticising of epoxides by polyester acrylates results in immobilisation of their oligomers in the space lattice of polyepoxide and is accompanied by the formation of clatharate polymer.

Linking of linear epoxide molecules into spatial epoxide groups occurs by the ionic mechanism or by means of cross-linking agents. In turn, the hydroxyl groups react with fatty acids, phenolic and carbamide resins and other products.

Catalytic hardening of epoxide resins is initiated by tertiary amines, resulting in a three-dimensional structure with simple ether bonds. From among the cross-linking semi-functional amines, only two aliphatic amines, viz., polyethylene polyamine and hexamethylene dyamine were used. Despite the fact that polyethylene polyamine is a hardener that can be used at both low and elevated temperatures, it suffers from major drawbacks such as toxicity, hygroscopicity etc. In view of this, the trend has increased in recent years to use oxyethylated polyamines UP-0622, and dioxyethyl diethyl triamine UP-0619. Aminophenolic hardener AF-2, which is synthesised from phenol, ethylenediamine and formaldehyde is employed for gluing wet surfaces and for making glued joints at subzero temperatures.

At the ‘Ukrainiplastmass’ Institute, researchers have developed imidazole hardeners that improve the technological and strength characteristics of epoxide compounds [56]. Some hardeners of the imidazole group are now produced on an ind...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Preface
• Table of Contents
• Section I Improving the Reliability and Durability of Structures and Constructions by using New Composite Materials
• Section II Glued Joints in Building Structures
• References