a novel hybrid system for floor beams

ICAMS 2010 - 3rd

International Conference on Advanced Materials and Systems

483

A NOVEL HYBRID SYSTEM FOR FLOOR BEAMS

MIHAI BUDESCU1, NICOLAE TARANU1, RALUCA HOHAN1,

IONUT-DAN GRADINARIU1

1 Faculty of Civil Engineering and Building Services, Department of Structural Mechanics,

Technical University "Gheorghe Asachi" of Iasi, 700050, Romania, [email protected]

The interest towards the ecological materials and the advanced technology have lead to the

recognition of a “hybrid” system that would substitute the traditional cement and develop superior qualities (strength and durability) in the construction works. This paper is based on an

experimental program regarding the properties of a composite with mineral matrix and glass fiber

bi-axial weave reinforcement. The hybrid system is composed of a mixture between cement, aggregate, water and a binder based on reactive anhydrous calcium sulphate. Preliminary material

tests have been made on samples similar to those made of mortar and convenient results have been

obtained. These samples showed an increased ductility compared to the traditional cement ones. The textile fiber reinforcement also increases the ductility and gives a warning signal when the

system is approaching the failure stage. Double T floor beams of different lengths have been tested

at four point bending to determine the mechanical properties and the structural response in

bending. The development of these systems aims to obtain new ecological products with increased

safety during service in terms of competitive prices. This particular system would help to valorize

the industrial gypsum waste which in our country is an unused raw material.

Keywords: hybrid system, composite, floor beams.

INTRODUCTION

Statistics present concrete as the main construction material in our country. The

continuously growing need for concrete raw materials leads to replacing of the natural

aggregates simultaneously with using local raw materials or industrial sub products. The properties of concrete are directly connected to the binder properties, so that the

future developments tend to increase the concrete strength, reduce the energy

consumption and use industrial waste in binder production.

For the purpose of saving Portland cement, in the production of which a large

quantity of work and energy is used, and to revaluate some industrial products emerged

the solution of introducing different active or passive admixtures during grinding, that

replace certain amounts of clinker. Generally, admixtures are called the substances that

added during the concrete production modify one or more properties of the fresh or

hardened concrete (setting time, workability, mechanical properties, impermeability,

colour or reducing the cement amount) (Ionescu I., Ispas T., 1997).

Progress of the main properties is needed so that concrete or micro concrete to remain competitive compared to other materials. Besides increasing the compression

strength other aspects like the cracking and tensile strength, acceleration of the setting

time for the initial hours and days and economical aspect must be enhanced.

In the past the strengthening of gypsum mortars was obtained with animal hair or

with straws for masonry elements. Nowadays natural or artificial fibres, randomly

distributed or weave, are used and thus obtaining an improvement for tension strength,

crack growth, dynamic loading, even an element cross-section reduction.

In Europe and as well worldwide the binders testing will be standardized which will

allow to characterize and use binders no matter the producing country. Development

will continue on the idea of construction systems with precast elements, completely

finished and equipped, so that the workflow of a house can be achieved in 2-6 days.

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484

THE DESCRIPTION OF THE HYBRID SYSTEM FOR FLOOR BEAMS

The process of achieving the constructive system consists in the making of a

monolithic structure by pouring the concrete in precast panels that are semi finished

plates with stiffeners (beams) reinforced with fiber glass weaves. These are poured

horizontally in special formworks once with an irretrievable formwork made of

polystyrene covered in fiber weaves.

Figure 1. Slab cross-section

The precast slab is made of:

a) polystyrene as an irretrievable formwork for the beams (see Figure 1) and also as

a support for the fiber glass weaves;

b) semi finished reinforced plates forming the inferior part.

The precast slabs with the same length as the span and a 60cm width are placed on

the walls without any other formwork or lifting devices, having for a 5m span and a

weight of maximum 70kg.

EXPERIMENTAL PROGRAM

The laboratory test described in this paper represents an initial pilot test. The test

was conducted to investigate the flexural behaviour of the proposed hybrid system for

floor beams. Due to the fact that in a building the spans are different, beams with

several lengths have been tested (Yanlei W., 2009).

Material Properties

Double T hybrid beams with mineral matrix were manufactured in the laboratory.

The composite material consists of a mixture of water, cement, sand (0-2mm) and an

ecological super-sulphatic binder (recently patented in France). Reinforcement was

made with three types of unidirectional E-glass fibers. Their properties are presented in

Tabel 1 (Task Group, 2006).

Table 1. Properties of materials

Density (kg/m3)

Tensile strength

(MPa)

Young modulus

(GPa)

Ultimate tensile strain

(%)

Thermal expansion coefficient

10-6/oC

Poisson’s coefficient

Binder 1600 40 13 - - -

E-glass 2500 3450 72.4 2.4 5 0.22

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485

Figure 2. Beam cross-section and fiber glass placement

On the exterior of the beam 5 layers of type (1) weave have been placed having the

mail dimensions of 10x10mm and a weight of 145g/m2. On the flanges two

supplementary layers of reinforcement have been added. The first exterior layer of type

(2) weave has the mail dimensions of 4x4mm, a weight of 160 g/m2 while type (3) has

10x10mm and 200 g/m2 respectively.

Test Set-up and Apparatus

Beams with an initial length of 5.1m were tested on bending, then their degraded areas were removed and beams with 3.6m and 1.5m respectively have resulted. These

double T floor beams of different lengths have been tested at four point bending. A

constantly increasing load was applied on the beam inducing longitudinal direct stress

and leading to the element failure. The test set-up is shown in Figure 3.

Figure 3. The experimental set up with LVDTs positioning

The LVDTs (D1 and D2) have been placed at the middle of the span on the inferior

flange of the beam to record the maximum displacement and warn if there is a buckling

of the web. To avoid local crushing at the loading and support areas steel plates of 10x15x0.5mm have been used. For the boundary and loading systems see Figure 4.

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Figure 4. Steel plates between beam and: a) support; b) load

EXPERIMENTAL RESULTS AND DISCUSSIONS

Through this experimental program values for the bending resistance and for displacement at the midspan have been obtained. Tests were made on two beams of

1.5m, one of 3.6m and one of 5.1m length summing a total of 4 experiments.

Load-Deflection Response and Failure Mode

For each beam the load-displacement curve is presented in Figure 5 and the

maximum values for loading and displacements are given in Table 2.

Figure 5. Load-displacement curves for different beam lengths

Table 1. Maximum values

Beams Fmax (KN)

Dmax (mm)

Gr. 1 50.2 15.6

Gr. 2 48.7 9.2

Gr. 3 22.3 23.4

Gr. 4 10.3 40.37

Behaviour of the 1.5m Beams

The crack appearance and development due to bending and its location, under the

load, are illustrated in Figure 6.

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487

Figure 6. Crack development in the 1.5m beam

The failure of the beam has been in a ductile progressive manner, with noise and the

fracture recorded in the maximum moment and shear force area. There was no local

crushing at the supports or at the load application region.

Behaviour of the 3.6m Beam

For the 3.6m beam the cracks appeared in the maximum moment area (see Figure 7).

Figure 7. Failure mode

The beam has a ductile behavior with cracks that develop progressively during the

load increasing on the entire maximum moment area. The fracturing was followed by

noise and there was no local crushing at the supports.

Behaviour of the 5.1m Beam

In this case a ductile behaviour has been noticed, with energy dissipation through a

map-cracking in the maximum moment area.

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Figure 8. Failure mode of the 5.1m beam with uncover of reinforcement

As it can be seen in Figure 8 failure is due to a crack that crosses the entire height of

the beam. As in the other cases the beam deflection is accompanied by noise presenting

no local crushing.

CONCLUSIONS

The following conclusions can be formulated from the experimental results:

- ductile behaviour with failure due to tension;

- cracks appear on the entire length of the beams, more concentrated in the

maximum moment area;

- fracturing preceded by noise;

- there is no local crushing in the loading and supports areas, which indicates

that the material has a good compression strength;

- failure occurred due to tensile stress.

Acknowledgement

This work was supported by CNCSIS - UEFISCSU, project number 737, PNII -

IDEI code 369/2008 on hybrid structures made of polymeric composites and traditional

building materials.

REFERENCES

Ionescu, I. and Ispas, T. (1997), Properties and Technology of Concrete, Technical Publishing House,

Bucharest.

Technical Agreement 008-01/076-2010, “Constructive Process and is Non Load-Bearing Multilayer Elements

With Kerysten® Binder, Reinforced With Glass Fiber Mesh (Synthetic)”.

Tehnical report, FRP reinforcement for RC structures, Task Group, 2006.

Yanlei, W., Qingduo, H. and Jimping, O., (2009), “Experimental Study on Hybrid FRP-Concrete Beam”,

FRPRCS-9, Australia. Ashour, A.F. (2006), “Flexural and Shear Capacities of Concrete Beams Reinforced with GFRP Bars”,

Construction and Building Materials, (20), 1005-1015.

Budescu, M., Taranu, N., Lungu, I., (2003), Building Rehabilitatin, Matei Teiu Botez Publishing House, Iaşi.

a novel hybrid system for floor beams

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