Konstantinos Zavliaris Ph.D., M.Sc., C.Eng., Greece
fib Symposium 2019. CONCRETE-INNOVATIONS IN MATERIALS, DESIGN AND STRUCTURES
May 27 – 29, 2019 | Krakow, Poland

1. Introduction

Laminates are thin composite materials. Composite materials consist of at least two materials that they interface with one another without dissolving or merge and act as one. The constituent components of laminates are the matrix, which is the continued phase incorporating the second phase which is the reinforcement, commonly fibres of different types and geometry. The properties of the composite material are superior to the properties of the individual materials from which it is constructed. The matrix bonds, protects and keeps the fibers in position and transfers the applied loads to the fibers, which are the main load bearing component of a composite material. The structural performance of the system is controlled, to a high degree by the bond between fibres and matrix.

2. Research Significance

The subject of the present experimental work was the structural behaviour of 1 to 2mm thin cement-based Laminates in tension. Such laminates can be bent around lightweight core to form sandwich or closed section composite elements with high strength and stiffness.

In order to achieve such a low thickness, ultra-fine materials should be used for the matrix and the adhesion between fibres and cement-based matrix had to be maximized,Figure 1.

The scope of this work included the effect of the properties of matrix, the amount of fabric reinforcement, and the type of polymer for the impregnation of fibres, the modification of cement matrix and as constituent material of interfacial grout, on the strength and strain of the laminate in tension.

3. The system

The laminate system investigated is shown below in Figure 1

Figure 1. Schematic structure of the cement laminate investigated

The two parts of the matrix were made of Cement I.52.5, ultra-fine limestone aggregates with d₉₅₌10 μm, microsilica and polycarboxylate water reducing agent. The mortar was modified by polymer mix.

In order to obtain the structural behavior of cement laminate in tension a series of tensile tests were carried out. The variables were: the mix design of the cement matrix, the amount of AR Glass fiber Mat reinforcement, and the type of polymer used as constituent material of penetrating grout and both the matrix and the interfacial mix. Two mixtures of cement-based matrix i.e mix BM, the basic cement-based matrix, and mix FM, three different percentages of AGFMat reinforcement – and two different types of polymers, were tested. The increased Reinforcement Percentage was achieved by successive Layers of Glass Fiber  glued on top of each other

The tests were carried out in accordance with ISO 527-2: 2012, the tensile specimens in form of dog-bone were 460mm long, 31-35mm wide in the middle and had variable thickness, subject to the number of layers of Glass Fiber Reinforcement.

The resulted failure stresses were normalized with respect to the amount of the Glass Fiber Reinforcement per unit width. Characteristic graphs of this normalized stress vs strain are shown in Figure 2 below

Figure 2. Relationship of Ultimate tensile stress normalized with respect to the value of reinforcement per unit width to strain.

4. Erection

From the test results obtained following conclusions can be deducted:

• Use of SAE leads to (25-30%) higher strain at peak of the Load and decrease in E modulus
• Matrix FM, resulted in 65% higher ultimate normalized stress in comparison with the basic cementitious matrix BM,
• The effectiveness of the Glass Fiber is strongly decreasing with the distance of each particular layer from the middle plane of the laminate.