Some Mechanical Properties of Ferro-Cement Mortar Modified byPolymer

Abdulkader Ismail A. Al-Hadithi, Khalil I. Aziz and Mohammed Tarrad N. Al-Dulaim

College of Engineering, University of Anbar, Ramadi, Al-Anbar, Iraq.

AbstractAbstract

The main aim of this work is to study the effect of adding Styrene Butadine Rubber (SBR) polymer on the mechanical properties of ferro-cement mortar. This kind of polymer was added with different weight ratios of polymerto cement (P/C), and these percentages were (3%, 7%, 10%). Reference mix was made for comparative reason. The following tests were made to investigate ferro-cement's mortars mechanical properties as followed: compressive strength, splitting tensile strength and flexural strength.Results demonstrated that in general, there is an improvement in mechanical properties due to adding SBR polymer and , all cement mortar specimens exhibited continuous increase in these properties with an increase of age . Incompressive strength, the increases due to modifying by polymer in 56 day age were (19.5% to 44.3%). In splitting tensile strength for the same age , the increases were (19.2% to 42.7%), whereas for flexural strength the increases were ( 5.9% to 19%).

Keywords: mechanical properties ,cement mortar, SBR polymer ,flexural strength

1-Introduction1-1-Ferro-Cement:

Ferro-cement has emerged asa viable structural material forthe use in such instance. Ferro-cement is a type of composite construction material in which abrittle cement-sand mortar matrix is reinforced with thin wire mesh, uniformly dispersed

throughout the matrix of the composite. Ferro-cement composite has been widely and successfully used for the construction of different structures which include silos, tanks, folded roofing, shells and bearing walls. (Narayanaswamy et al, 1981 ; Al-Rifaie et al , 1994 ; Al-Rifaie et al , 2001). Ferro-cement is a composite material

used in building with cement, sand, water and wire mesh material. It is fireproof, earthquake safe and does not rust, rot or blow down in storms. It has a broad range of applications which include components in a building, repairof existing building.

1-2-Classification of Concrete Polymer Composites:

Concrete polymer composites are generally classified into the following types in terms of process technology.(Ohama,1997) (a) Polymer Impregnated Concrete(PIC).(b) Polymer Mortar and Concrete (PM and PC)(c) Latex Modified Concrete (LMC).

1-2-1- Polymer Modified Concrete(PMC)

It is produced by incorporating a monomer, polymermonomer mixture, or a dispersed polymer (Latex) into a cement concrete mix. To affect the polymerization of the monomer orprepolymer monomer, a catalyst is added to the mixture. (Ohama,1996) In all cases, the mixing and handling of PMC is similar to conventional Portland

cement concrete and mortar materials. It exhibits excellent bonding to steel reinforcement and old concrete, good ductility, resistance to penetration of water and aqueoussalt solutions and resistance tofreeze-thaw damage. Its flexuralstrength toughness and creep arehigher than that of plain concrete. The drying shrinkage is generally lower than that of conventional concrete. (Al-Qadi et al,1993)

2-Materials and Methods

The experimental program was planned to investigate the effect of using polymer on the mechanical properties of Ferro-cement mortar.

2-1- Materials:

2-1-1- Cement: The cement used through this work was Ordinary Portland Cement type I and it is conform to the Iraqi specification No. 5/1999.(Iraqi specifications - No(5), 1999)

2-1-2- Fine Aggregate:

Natural yellow sand conforming to the Iraqi StandardN0.45(Iraqi specifications - No(45), 1999) grading

requirements (zone-2) was used in production of concrete specimens used in this study.

2-1-3- Mixing Water:

Ordinary drinking water was used for mixing and curing for all specimens. 2-1-4- Polymer:

Styrene Butadiene Rubber (SBR) is used as polymer modifier in this study. Styrene Butadiene, an elastomeric polymer, is the copolymerized product of two monomers, Styreneand Butadiene. Latex is typically included in concrete in the form of a colloidal suspension polymer in water.The polymer (SBR) was used as a ratio by weight of cement of 3%,5% and 10%.

2-3- Preparation of Mortar Specimens:

Four groups of mixes wereused in this research. All proportions were (1:2) cement: sand. 2-4-Mix Preparation: A mechanical mixer of thecapacity (0.1) m3 operated by electrical power was used, the fine aggregate and cement were

added before adding polymer and dry mixing were continued until the dry mix became homogenous, then the polymer was added untilall particles are fully coated with polymer and finally water were added and mixing continues until uniform mix is obtained, this procedure is similar to the method used by Ohama .(Ohama,1997)

2-5- Determination of the Workability:

Workability of all types of Mortar was measured by slump test according to the procedure described in ASTM C143-89. .(Annual Book of American Societyfor Testing and Materials, 1989)The Water/Cementations materialsratios were adjusted to maintainon workability. 2-6-Casting, Compaction and Curing:

The molds were lightly coated with mineral oil before use according to ASTM C192-88 . For cubes, cylinders and prisms casting was carried out in different layers each layer is of 50mm. Each layer was compacted by using a vibrating table for (15-30) second until no air bubbles emerged from the surface of the mortar, and the

mortar is leveled off smooth to the top of the molds.

2-7- Compressive Strength:

Compressive strength was determined using of (100×100×100)mm cubes according to B.S. 1881 , Part 116. (British Structural Institute BSI,1983)

2-8-Splitting Tensile Strength:

The splitting tensile strength test was carried out inaccordance with ASTM C496-86.(Annual Book of American Societyfor Testing and Materials, 1986)Cylinder specimens of (150*300) mm were subjected to compressionloads along two axial lines which were diametrically opposite. The load is applied continuously until the specimen failed. The compressive loading produces a transverse tensile stress which is uniform along the vertical diameter.

2-9- Flexural Strength :

According to ASTM (192-88).(Annual Book of American Society for Testing and Materials,1988) concrete prisms of (100×100×500) mm were prepared and two point load testwas carried out according to ASTM (C-78-84). .(Annual Book of

American Society for Testing andMaterials, 1984)

3-Results and Discussion

3.1- Compressive strength :

The relationship between compressive strength at different ages and (P/C) ratio is shown in Figure (1). Results demonstrated that in general allcement mortar specimens exhibited continuous increase incompression strength with increase of curing age and we can notice that the compressivestrength increases with increaseof (P/C) ratio. That increase in compressive strength might be due to three facts; the first isthat polymer-modified cement mortar has less W/C ratio, whichgives higher strength. The second is that, the use of SBR polymer leads to form a continuous three-dimensional network of polymer molecules throughout cement mortar which increases the binder system due to good bond characteristics of SBR polymer. The last is partial filling of pores with polymer which reduces the porosity, and hence increases the strength. (Ohama,1998) The increase at compressive strength with increase of curing ages can be

explained by completion of polymerizing reaction of SBR polymer within these ages, in addition to continued reaction of the hydration process. The hydration of cement isresponsible of strength at earlyand latest age in reference mixes. The hydration operation is responsible for this strength; therefore, the difference between compressive strength of reference mixes and other mixes is smaller at early ages and becomes larger at latest ages. Whereas, for cementmortar mixes containing polymer both the cement hydration and production of polymer film by polymerization are responsiblefor strength gain.( Al-Hadithi,2005) So at early ages for (PMM), the polymerization operation is at the beginning with low hydration development, after that both hydration and polymer film production will develop causing increasing compressive strength and then increasing the difference between polymer modified mortar and reference mixes. The polymerfilm will behave as a container of water needed for reaching cement hydration at advanced steps.(Al-Hadithi,2001) The specimens made from mixes containing polymer with different percentage seem to be

less damaged at failure when compared with these made from reference mixes. This might be due to the effect of increasing the bond among particles by polymer film.

The highest magnitude of compressive strength at (7) daysage is (43.5 MPa) for concrete specimens and the highest magnitude of compressive strength at (28) days age is (50.2 MPa), while at (56) days age, the respective highest magnitude is (53.4 MPa) , all these magnitudes occurred with P/C ratio of (10%). The histogram of the development of compressive strength with age for various P/C ratio is shown in figure (2).

Figure 1.Relationship between Compressive Strength andAge for Various P/C Ratios

Figure 2. Development of Compressive Strength

with Age for Various P/CRatios.

3-2-Splitting Tensile strength:

The value of splitting tensile strength obtained from tests on (100×200) mm cylindrical cement mortar specimens after curing age of 7,28,56 days. Figure (3) shows the development in splitting tensile strength of cement mortar specimens with and without polymer. The results indicated that all types of cement mortar specimens exhibited continued increase in

splitting tensile strength with development of curing ages. From Figure (3), it can be seen that the splitting tensile strength increases with an increase in (P/C) ratio for all specimens at different ages.This increase may be due to the reduction in W/C ratio, contribution of high tensile

strength by the polymer itself and the increase may be ascribedto the reduction in capillary porosity of the cement matrix because of using the SBR polymerwhich fills the voids in concrete. (Letif,1998 ; Folic,1998) At (7) days age the highest magnitude of splitting tensile strength is (5.64 MPa) for cement mortar specimens with(10%) P/C ratio, and at (28) days age the highest magnitude of splitting tensile strength is(6.85 MPa) for cement mortar specimens with (10%) P/C ratio while at (56) days age the highest respective magnitude is (6.88 MPa) for cement mortar. The histogram of the development of splitting tensilestrength with age for various P/C ratios is shown in Figure (4).

Figure 3.Relationship between Splitting Tensile Strength and Age for Various P/C.

Figure 4. The Development of Splitting Tensile Strength with Age for Various P/C Ratios

3-3- Flexural strength

The flexural strength was determined at ages of (7), (28) and (56) days for moist cured cement mortar prisms of (100×100×500) mm dimensions. Theresults indicated that flexural strength increased with development of curing ages, alsothe flexural strength increased with the increase in P/C ratio at all ages for different types of mortar mixes. From Figure (5), it can be seen that, this increase in flexural strength isattributed to the reduced capillary porosity caused by thereduction of water content of the mix because of adding the polymer to that mix in addition to dispersion of the cement agglomerates into primary particles. Further, the dispersion system will include

particles spaced at more uniformdistance from one another. Thereby on continuing hydration there is a greater statistical chance of intermeshing of hydration product with fine aggregates surface to produce a system of higher internal.

Figure 5. Relationship between Flexural Strength and Age for Various P/C Ratios.

At (7) days age the highest magnitude of flexural strength is (5.63MPa) for specimens with (10%) P/C ratio, at (28) days age the highest magnitude of flexural strength is (5.77MPa) for specimens with (10%) P/C ratio while at (56) days age, the highest respective magnitudeis (5.81MPa) for specimens with (10%) P/C ratio. The histogram of the development of flexural strength with age for various P/C ratios is shown in figure (6).

Figure 6. The Development of Flexural Strength with Age for Various P/C Ratios

4-Conclusions :

Based on the extensiveresearch works the followingconclusions can be drawn:

1- The mechanical propertiesof polymer modified cementmortar had shown a clearincrease in general due tothe inclusion of SBR latexfor specimens. The increaseof P/C ratio from 3% to 10%had resulted in:-

A- For Compressive, SplittingTensile and Flexural Tests:(a) An increase in the 7 daycompressive strength from 31.6N/mm2 for reference mix to 37.8N/mm2 (P/C = 3%), to 40.2 N/mm2

(P/C = 5%) and to 43.5 N/mm2 (P/C= 10%).

(b) An increase in the 28 daycompressive strength from 35.2N/mm2 for reference mix to 42.5N/mm2 (P/C = 3%), to 49.8 N/mm2(P/C = 5%) and to 50.2 N/mm2 (P/C= 10%).(c) An increase in the 56 daycompressive strength from 37N/mm2 for reference mix to 44.2N/mm2 (P/C = 3%), to 51.7 N/mm2

(P/C = 5%) and to 53.4 N/mm2 (P/C= 10%).(e) An increase in the 7 daysplitting tensile strength from4.61 N/mm2 for reference mix to5.36 N/mm2 (P/C = 3%), to 5.4N/mm2 (P/C = 5%) and to 5.64N/mm2 (P/C = 10%).(f) An increase in the 28 daysplitting tensile strength from4.74 N/mm2 for reference mix to5.55 N/mm2 (P/C = 3%), to 6.32N/mm2 (P/C = 5%) and to 6.85N/mm2 (P/C = 10%).(g) An increase in the 56 daysplitting tensile strength from4.82 N/mm2 for reference mix to5.78 N/mm2 (P/C = 3%), to 6.56N/mm2 (P/C = 5%) and to 6.88N/mm2 (P/C = 10%).. (h) An increase in the 7 dayflexural strength from 4.56 N/mm2

for reference mix to 5.03 N/mm2

(P/C = 3%), to 5.12 N/mm2 (P/C =5%) and to 5.63 N/mm2 (P/C =10%).(i) An increase in the 28 dayflexural strength from 4.6 N/mm2

for reference mix to 5.11 N/mm2

(P/C = 3%), to 5.14 N/mm2 (P/C =

5%) and to 5.77 N/mm2 (P/C =10%).(j) An increase in the 56 dayflexural strength from 4.88 N/mm2

for reference mix to 5.17 N/mm2

(P/C = 3%), to 5.24 N/mm2 (P/C =5%) and to 5.81 N/mm2 (P/C =10%).

2- This increase in mechanicalproperties may be attributed to continuous polymer network formed within the mortar body, theimproved bond between hydration products and polymer

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