Factors Affecting Compatibility between (S.B.R) Polymer Repair Materials and Concrete Substrate

In this stu dy, the compatibility of polymer modified r epair m ortar and substrate concrete was investigated in three stages. First stage includes studying the individual pr operties of polymer and con ventional repair materials, and also two types of conc rete, such as compressive strength, split tensile strength, and flexural strength using standard ASTM test procedure. Second stage includes evaluating the bond strength of composite cylinder for different combinations of repair materials and substrate concrete. Third stage includes investigating the compatibility using a composite beam of repair material and substrate concrete under third point loading. The experimental resul ts show tha t the compressive strength, split tensile strength an d flexural stre ngth is not a c rucial factors f or the success of concrete repair system. While bond strength tests are pro vide strong indication about t he compatibility. The bond strength of S.B.R polymer material prod uced by Al-Khaleej Company was not strong enough to be recomme nded t o use for co ncrete repairing systems.

) emulsion was used throughout this study as a polymer admixture to produce polymer modified mortar.

Substrate Concrete
Two substrate concrete mixes were used in this study.One mix considered to be low quality substrate, while the other one considered being normal quality substrate.The mix proportion of the concrete is the same, (1:1.6:2.9 by wt.).The deference is only in w/c ratio, which was 0.4 for normal strength concrete 0.6 for low strength.British standard method was adopted to design the normal quality concrete (named as C 25 ), while the low quality concrete (named as C 15 ) was achieved by increase the water cement ratio by about 50% as compared to C 25 .

Concrete Repair Materials
Repair material M c (named as conventional mortar) was a blend of Portland cements with sand.The mortar was proportioned to have a cement-tosand weight ratio of 1:2 with a water to cement ratio of 0.5.Repair material M S.B.R , polymer modified mortar, was prepared by adding S.B.R (15 % of cement by weight), this ratio has been chosen according to previous investigation [7].The w/c was 0.52 to obtain close flow (100-110%).The cement to sand ratio was the same as in normal mortar.All specimens were cured in water until the age of 28 days, except the M S.B.R specimens cured in air dry which is mandatory for polymer to get hardening [8].

Workability
The flow of the repair materials was determined using flow table of mortar as per ASTM C 230-03[9] standard practice.Flow was measured immediately after mixing, within 5 minutes from the time of addition of water into the mix.

Compressive Strength
The compressive strength of the different repair mortars was determined using 50 mm cube.compression at 1 and 28 days age.The average of three cubes was recorded for each testing age.

Split Tensile Strength
The split tensile strength of the substrate concrete and the repair materials was determined using 100×200mm cylinders as per the ASTM C496-04 [11] test procedure.The split tensile strength of the repair materials and substrate concrete were tested at 1 and 28 days age.The average of three specimens was recorded for each testing age.

Flexural Strength
The flexural strength was determined using the third point loading beam method.The prism sample dimensions were 100×100×400mm, as per ASTM C78-02 [6].The flexural strength of the substrate concrete and repair materials were tested at 1 and 28 days age.

Bond Strength
The bond strength of the repair materials was determined using the standard ASTM C882-99 test procedure [12].In this test procedure, the repair material is bonded to a substrate concrete specimen on a slant elliptical plane inclined at 30° angle from vertical to form a 100×200 mm composite cylinder (see Fig 1).Before the repair material is bonded to the substrate concrete, the slant surface of the substrate concrete specimen is cleaned and dried.The test is performed by determining the compressive load required to fail the composite cylinder and the bond strength is calculated as [Max Load] / [Area of Slant Surface].

3.7
Third Point Loading Composite Prism Test.
In this test method, concrete prisms 400mm in length with a cross-section of 100mm by 100mm were cast as per standard ASTM C 78-02 test procedure.The composite prism for evaluating the compatibility of repair material with substrate concrete was fabricated to the same dimensions as the control prism, with the exception that a wide-mouthed notch 200mm (length) × 100mm (width) × 10mm (thick) was cast into the bottom of the composite prism using a 3-dimensional inset (Fig 2).After de-molding, the prisms were moist cured for 28 days, and then the wide-mouthed notch areas were textured using dry brushing.The rough surface textured substrate specimens were air-dry cured for 7 days before batching the notched area with the repair materials.The composite sections were demolded next day and cured in water for 28 days.After 28 days, the composite sections were tested in third point loading prism test, as per ASTM C78-02 test procedure.

Results and Analysis. 4.1 Mechanical Properties
Table 2 shows the compressive strength, split tensile strength, and flexure strength of the repair material and substrate PDF created with pdfFactory Pro trial version www.pdffactory.comconcrete.These values are the average of strengths of three samples.
All the strengths found increasing from 1 to 28days.Both repair materials have similar compressive strength at 28 days which is intended to be in equal starting point, while the degree of compatibility enhancement will show the influence of other factors.
The mix proportion of both concrete substrates is the same with the exception of w/c ratio.As a result two types of concrete have been made to simulate the real condition of weak and normal strength substrate concrete, C 15 and C 25 (see section 3.2).
The degree of improvement in compressive strength from 1 to 28 days was found to be 75% and 80% for substrate concrete C 15 and C 25 respectively.Since the proportion of both C 15 and C 25 are the same with the exception of w/c ratio, then this behaviour is related to the differences in w/c ratio.In contrast, test specimens of both repair materials (M c and M S.B.R ) exhibited a same gain in compressive strength (i.e.89.9%) with 28 days.Figure 3 shows the development in strength of the substrate concrete and the two repair materials considered in this study.
It is apparent from observing the data in Figures 3, a, b and c that depending on the specific repair material, significant difference exists between the properties of the repair material and the substrate at any given age.This disparity in strengths can be expected to influence the failure mode and the bond strength determined in the composite cylinder.And also influences the load carrying capacity of the composite beams (this matter will discuss later in section 4.2).
Furthermore, Table 2 and Figure 3 show that differences exist between the properties of the repair materials M S.B.R and M C were not the same all the time.The degree of enhancement was 1.5%, 3.6%, and 12.7% for compressive, split tensile and flexural strength respectively, at 28 days age.This wide range of differences make difficulties to decide wither these differences is significant or not.So, statistical approach has been used to handle the data, and a T test was adopted to compare the average mean values, Table 3 shows the results.
According to statistics principle [13], a ρ-value greater than the significant level α (i.e 0.05) signifies that no significant difference exists between the measured two values.For instance, ρ-value = 0.035 which is less than 0.05 signifies the difference in compressive strength values between M C =19.6 MPa and M S.B.R =19.9 MPa.Hence, the PDF created with pdfFactory Pro trial version www.pdffactory.com

Compatibility Results
It is well established that a prism of higher total depth value deflects less in the flexure test compared to a prism of lower depth value under the same loading.In the composite prism, if the repair system is failed in bond, and there is a de-bonding between the batched notched area and the substrate, the total depth will be reduced, and the load deflection curve should have lesser slop than the slop of the load deflection curve of compatible composite prism (i.e without de-bonding) as shown in Figure 7. Otherwise, the load will transfer to repair material, and the composed prism consider compatible.
Table 4 shows the bond strength, and third point strength of composite beams.These values are the average of strengths of three samples.
Due to the higher split tensile and flexural strengths of M S.B.R than M c , it is expected that the third points test results of M S.B.R will be more than M c results too.In contrast, The authors believe that this weak behavior of bond strength of S.B.R specimens are related to the trade mark of the chosen type of S.B.R product (i.eProduce by Al-Khaleej Company trade mark), and other products of S.B.R available in the local markets, need to be investigated.

Conclusions
Based on the results from the experimental program it can be concluded the following: 1.Using S.B.R will improve the compressive split and flexural strength of M Figure (1) Substrate and Composite Section for Slant Shear Bond-Strength Test.

Figure
Figure (2) Third Point Loading Composite Beam.

Figure ( 5 )
Figure (5) Mixed Failure Mode of M c with C 15 Composite Cylinder Specimens at 28 Days Age.

Figure
Figure (6) Slant Shear Failure Mode of M S.B.R with C 25 Composite Cylinder Specimens at 28 Days Age.

Figure
Figure (9) Prism Composed of C 25 Repaired by M S.B.R , 28 Days Age.

Table 4
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Table (3): Statistical T-test Results for Average Strength Comparison Compression strength 28 days (MPa) Split tensile strength 28 days (MPa)
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