Experimental Evaluation of Elastic Modulus of Unreinforced and Glass

Experimental Evaluation of Elastic Modulus of Unreinforced and Glass Fibre Reinforced Mineral Matrix Composite George TARANU

Technical University “Gheorghe Asachi” of Iasi, Romania [email protected]

Ionut Ovidiu TOMA

Technical University “Gheorghe Asachi” of Iasi, Romania [email protected]

Raluca PLESU

Technical University “Gheorghe Asachi” of Iasi, Romania [email protected]

Ionut Dan GRADINARIU

Technical University “Gheorghe Asachi” of Iasi, Romania [email protected]

Mihai BUDESCU

Technical University “Gheorghe Asachi” of Iasi, Romania [email protected]

Conference Topic – CT 7 Construction Abstract The paper presents the results of an experimental program on the elastic modulus of an unreinforced mineral matrix and glass fibre reinforced mineral matrix composite (GFR MMC). One type of E-glass alkali resistant bidirectional reinforcement mesh was used. The mineral matrix is a combination of sand, Portland cement and calcium sulphate βanhydride III’. Three different mixtures have been cast in cylinders with a ratio height/diameter of 2/1. The first mix proportion is a combination of sand and Portland cement and represents the reference mix. The second and the third are combinations of sand, Portland cement and calcium sulphate in the β-anhydrite III' form. This anhydrous sulphate has an important influence on the workability of the resulting mineral matrix so it can be cast over the glass fibre reinforcing mesh. All the specimens were tested in compression and the elastic modulus as secant was evaluated for each one. In conclusions the obtained results consisting of stress-strains curve and Young modulus in compression are discussed and compared. The obtained results will be useful in FEM of structural elements in addition of tensile results and also these show that the technology of glass fibre reinforced mineral matrix composite material is proper to obtain structural elements like shear wall panels or horizontal panels in case of low cost houses or shelters.

Key Words: glass fibre reinforced mineral matrix; Portland cement; Young modulus, anhydrous calcium sulphate

Introduction In the past decades, composite materials represent an important segment for construction materials. They have been used especially for rehabilitation and strengthening of old structures but the research works showed that, they are also appropriate for new structures like civil structures, houses, shelters a.s.o. The incorporation of synthetic fibres (e.g glass fibres) in cement mineral matrix leads to a new composite material with improved mechanical and elastic properties. It can be used for making structural elements. The mineral matrix is good in compression but it is weak in tension. The role of fibres is to improve de overall strength of the composite material. Glass fibres are an appropriate choice due to low production costs and high strength in tension. These fibres are available in different wire types: unidirectional or bidirectional meshes, chopped fibres or other textile types. The bidirectional mesh is the best choice when it comes INTERNATIONAL CONFERENCE ON ENGINEERING UBI2011 - 28-30 Nov 2011 – University of Beira Interior – Covilhã, Portugal

to reinforcing structural elements made of mineral matrix. This is mainly due to the fact that it can reduce the crack formation is virtually any direction. Different types of prefabricated structural panels can be obtained by using such reinforcement combined with a highly fluid mineral matrix. These panels can form structures for houses or different types of shelters. The main advantages of these structures are the relatively light weight compared to traditional reinforced concrete or even load bearing masonry structures, good resistance to seismic loads and their long term durability. Additionally, the short erection time and the reduced labour lead to a low cost structure. In order to be able to correctly anticipate the behaviour of elements and structures under different loading scenarios, in design models with FEM it is necessary to investigate the mechanical properties of the materials their components are made of. The present paper presents the results obtained from laboratory investigations on the mechanical and elastic properties of a composite mineral matrix based on partial replacement of the ordinary Portland cement by an equivalent binder in the form of anhydrous calcium sulphate (1, 2, 3). Elastic modulus and the compression strength were chosen because in FEM design these are main parameters necessary. Experimental tests Three mix proportions were used for the determination of compressive and tensile strengths. The mineral matrix is the result of combining sand 0-2 mm with ordinary Portland cement CEM /A-S 32.5 R and anhydrous calcium sulphate in the β-anhydrite III' form. The anhydrous calcium sulphate is a hydraulic sulphated binder obtained exclusively from industrial waste, mostly non-recycling materials, stored in huge deposits above ground (phosphogypsum, lactogypsum, citrogypsum and Flue Gas Desulfurization gypsum). This binder is relatively new (patented in 2008 in France) and its obtaining process makes it possible to be entirely recyclable. The production process runs at low temperatures under ˚C and 700 is CO 2 emissions free (4). Table 1 presents the percentages of the mineral matrix components used in the mix proportions. Testing methodology All components have been mixed in dry condition while water was added later using the mixer dosimeter. In the first stage the fluid mix has been cast in 5 cylinder moulds, especially designed with a height/diameter ratio of 2/1. In the second stage the fluid mix were cast over the glass fibre reinforcement mesh. The glass fibre reinforcement (GFR) is a wired network with 5x5 mm distance between wires and with a section of 1 mm x 0.5mm of wire. The glass fibre reinforcement was arranged in 5 layers at the exterior of cylinders in the manner shown in Figure 1. In figure 1 is presented 1 layer of glass fibre reinforcement mesh. All 5 layers are circumferential distributed with a total length of the horizontal wires of 1000 mm. Table 1- Mixtures of mineral matrix Spec. no.

Label

Sand (%)

0 1 2

NCK 50/50/0 NCK 50/25/25 NCK 50/35/15

50 50 50

Portland cement (%) 50 25 35

Calcium sulphate (%) 0 25 15

Water/Total ratio 0.40 0.40 0.40

Tests consisted of determining the mechanical strength and Young’s modulus in compression of each mixture. The testing ages was 7 days because the recent research works show that this special binder has a very good early age performance (5, 6). This is, indeed, suitable for structures which require a very short construction time interval. The machine where specimens where tested has an extensometer which meets the requirements of Accuracy Class 0.5 to EN ISO 9513 with long sensor arms. INTERNATIONAL CONFERENCE ON ENGINEERING UBI2011 - 28-30 Nov 2011 – University of Beira Interior – Covilhã, Portugal

Figure 1- The composition of the specimens

The accuracy of macro extensometer is from 20µm and is given by the calibration report. The total displacement where measured with the own machine displacement transducer and strains are calculated by the macro extensometer. The strain recorded by the macro extensometer is related to the initial length between contacts which is 50 mm. The Elastic Modulus was evaluated as secant for round specimens with the formula: E = [4 * L0 * (XH - XL)] / [pi * d² * (LH - LL)]

(1)

E: Compression modulus in N/mm² or MPa L0: Initial gage length in mm = 50 mm XH: End of compression modulus determination in N (0.4*fc) XL: Begin of compression modulus determination in N (at 0) pi: 3.14159 d: Diameter in mm LH: Strain in mm at XH LL: Strain in mm at XL The testing machine used is a Universal Materials Testing Machine ZWICK/ROELL model MTM SP 1000 which has a capacity of 1000 kN. The tests were force controlled with the rate of loading by 0.225 MPa/s. Results The first results obtained at 7 days were of the specimen type 0 - NCK 50/50/0. This mixture represents the reference sample. In figure it is showed the specimen equipped with the displacement transducer. The stress–strain envelope curve in compression of NCK 50/0/0 – 7d specimen is presented in Figure 3. The average value of Young’s modulus obtained was 3466 MPa. The reference mixture was tested unreinforced because, due to its viscosity, cannot be cast over the reinforcing mesh. In order to achieve this, higher water/binder ratio would have been needed. The obtained results will be later used as comparison basis for the fluid mixtures based on calcium sulphate in the β-anhydrite III' form. Five specimens were made for each mix proportion. Figures 5 and 7 present the stress-strain curves for NCK 50/35/15 and NCK 50/25/25 unreinforced mixtures at the age of 7 days while figures 4 and 6 present aspects during the tests. The experimental values obtained show that the increase of the percentage of anhydrous calcium sulphate leads to a decrease in the values of the longitudinal modulus of elasticity. While the reference specimen had an average value of Young’s modulus of 3466 MPa, the NCK 50/35/15 and NCK 50/25/25 led to values of Young’s modulus of 3334 MPa and 3285 MPa, respectively. INTERNATIONAL CONFERENCE ON ENGINEERING UBI2011 - 28-30 Nov 2011 – University of Beira Interior – Covilhã, Portugal

Figure 2 - Image during the test of NCK 50/50/0 specimens

Figure 3 - Stress-strain curve of NCK 50/50/0-7d unreinforced

Figure 4 - Image during the laboratory test of NCK 50/35/15 specimens

Figure 5 - Stress-strain curve of NCK 50/35/15-7d

Figure 6 - Image during the laboratory test of NCK 50/25/25 specimens

Figure 7 - Stress-strain curve of NCK 50/25/25-7d

This means that for a given cross-section, the structural elements made with the composite mineral matrix have almost same stiffness than structural elements made with conventional mineral matrices. The calcium sulphate affect the behaviour of mineral matrix in terms of strength which is increased, but also increase the deformability making the material more ductile. The specimen reinforced circumferential with 5 layers of glass fibre bidirectional mesh (GFRNCK – glass fibre reinforced NCK) behaved differently from the unreinforced ones. The stressstrain curves are given in Figures 9 and 10 for the NCK 50/25/25 and NCK 50/35/15 mixtures while the figures 6 and 8 present the specimen tested and the failure of these. In case of GFR NCK 50/35/15 the maximum strength in compression obtained was 24.1 MPa smaller than the strength of GFR NCK 50/25/25 which results 25.8 MPa. INTERNATIONAL CONFERENCE ON ENGINEERING UBI2011 - 28-30 Nov 2011 – University of Beira Interior – Covilhã, Portugal

Figure 2 - Image during the GFR-NCK 50/35/15 specimens test

Figure 9 - Stress-strain curve of reinforced specimen GFRNCK 50/35/15-7d

Figure 10 - Stress-strain curve of reinforced specimen GFR-NCK 50/25/25-7d

Figure 11 – Comparative stress-strain curves of specimens tested at age of 7 days

The average modulus of elasticity in compression was 4041 in case of the specimen with higher percentage of cement while the others had obtained a value of 3540 MPa. The failure of specimen after the maximum strength was achieved consists in shear of the glass fibre reinforcement mesh. This was split in the middle area. The transversal (radial) wires of the mesh were broken from tensile stresses while the longitudinal one parallel with the force applied failed due to shear stresses. In figure 11 are presented the comparative stress strain curves of all the specimens tested. In table 2 are presented the average values of elastic modulus in compression obtained on all the specimens tested.

INTERNATIONAL CONFERENCE ON ENGINEERING UBI2011 - 28-30 Nov 2011 – University of Beira Interior – Covilhã, Portugal

Table 2- Average values of elastic modulus of the mixtures Mixture NCK 50/50/0 NCK 50/35/15 NCK 50/25/25 GFR-NCK 50/35/15 GFR-NCK 50/25/25

Emod MPa 3466 3334 3285 4041 3540

It can be observed that the smallest strength in compression is of the reference specimen where the calcium sulphate is not present. Increasing the percentage of calcium sulphate the strength also increase but the elastic modulus decrease. In case of the same percentage of calcium sulphate like Portland cement one (NCK 50/25/25) the strength is greater but the elastic modulus decrease. That means the mixture of mineral matrix is more ductile. Reinforcing the mixtures with glass fibre mesh it was observed that not just the strengths are increased but also the elastic modulus has an increasing of 17.5% from the unreinforced mixtures. The GFR NCK 50/25/25 has an increasing of elastic modulus of 7.2% from the unreinforced mixture but is with 12.4% smaller compared with GFR NCK 50/35/15. Conclusions In this paper a partial results of an extensive experimental program on unreinforced and glass fibre reinforced mineral matrix are shown. The research program focuses on using the technology of mineral matrix composite materials to obtain structural elements as prefabricated panels for low cost houses or shelters. Three different mixtures have been tested, leading to five analysis cases. The importance of determining the strength and the elastic modulus in compression consist in use of these parameters in FEM design of structural elements. The specimens where tested in a ZWICK/ROELL 1000 kN universal testing machine with an accuracy Class 0.5 to EN ISO 9513. The tests were force controlled with the rate of loading by 0,225 MPa/s. The elastic modulus was determined as a secant modulus from origin to 0.4*fc. The test results have shown that the elastic modulus has increased in case of glass fibre reinforced mineral matrix but also in case of unreinforced mixtures in comparison with the reference mixture where calcium sulphate is not present. The age of 7 days was chosen because of the necessary short time erection which results low cost production for the structures. The experimental study shows that the technology of composite material can be successfully applied in case of mineral matrix and glass fibre reinforcement mesh to make structural elements like horizontal panels or shear wall panels. The glass fibre reinforcement mesh makes the structural elements made with composite mineral matrices and reinforced with bidirectional glass fibre meshes, more efficient in seismic active areas as they are able to dissipate more energy during the occurrence of an earthquake. In the same time high strength vs. light weight of entire structure is an important advantage in terms of inertial masses. The results provided in this article can be used in FEM of structural elements or structures in addition of tensile properties. Acknowledgments This paper was supported by the project "Develop and support multidisciplinary postdoctoral programs in primordial technical areas of national strategy of the research - development innovation" 4D-POSTDOC, contract nr. POSDRU/89/1.5/S/52603, project co-funded from European Social Fund through Sectorial Operational Program Human Resources 2007-2013.

INTERNATIONAL CONFERENCE ON ENGINEERING UBI2011 - 28-30 Nov 2011 – University of Beira Interior – Covilhã, Portugal

References

(1) Ali Libre, N., Shekarchi, M., Mahoutian, M., Soroushian, P. “Mechanical properties of hybrid fibre reinforced lightweight aggregate”, Elsevier, Construction and Building Materials, Vol. 25, (2011), pp. 3066 - 3072. (2) Bejan, L., Taranu, N., Sarbu, A. 9, , “Advanced polymeric composites with hybrid reinforcement”, Journal of Optoelectronics and Advanced Materials, Vol. 12, (2010), pp. 1930 - 1934. (3) Singh, M., “Use of industrial by-products in the manufacture of cement and alternative binders”, Indian Cement Review, (1993), pp. 119 - 128. (4) “Process for the Industrial Manufacture of Compositions Based on Anhydrous Calcium Sulphate in the B-Anhydrite III’ Form, and Corresponding Compositions and Binders”, WO 2010/003827 A1, France, January 2010. (5) Taranu, G., Toma, I. O., Plesu, R., Grădinariu, I. D., “Experimental Evaluation of Mechanical Properties of Cement and Calcium Sulphate Mineral Matrix”, Bulletin of the Polytechnic Institute of Iasi. Construction and Architecture Section. (2011), Vol. LVII (LXI), 2, pp. 131 - 140. (6) Toma, I. O., Covatariu, D., Taranu, G., Budescu, M., “Early-Age Mechanical Properties of Mortars with Different Percentages of Eco-Cement”, Bulletin of the Polytechnic Institute of Iasi. Construction and Architecture Section. (2011), Vol. LVII (LXI), 2, pp. 155-166.

INTERNATIONAL CONFERENCE ON ENGINEERING UBI2011 - 28-30 Nov 2011 – University of Beira Interior – Covilhã, Portugal