Philippine Science High School Main Campus
Different Textiles and Designs for Fabric Reinforced Concrete
Alfonso Elias C. Lopez Darren James F. Judi Justin Marius Marius D. Morales Morales
March 2012
Different Textiles and Designs for Fabric Reinforced R einforced Concrete by Alfonso Elias C. Lopez Darren James F. Judi Justin Marius Marius D. Morales Morales
Submitted to the Faculty of the Philippine Science High School – Main Campus in partial fulfillment of the requirements for Science and Technology Research 2 March 2012
Lopez, AEC, Judi, DJF & Morales, JMD. (2012). “Different Textiles and Designs for Fabric Reinforced Concrete”. Research Paper. Philippine Science High School – Main Campus. ABSTRACT
Concrete, being a critical building material, must be reinforced. The common method is with steel rebar, but this may prove too costly for some applications. This project aimed to test the possibility of reinforcing concrete with fabrics, and to compare the strength of three textiles: denim, muslin and spandex for their applications in reinforcement. Two sets of three replicates of four treatments (including control) were used. Each sample was in the form of a concrete beam reinforced with a fabric (or for control, not reinforced at all). One set was reinforced by individual large cylinders of fabric, and the other was with many small strips. Each beam was poured and cured for seven days, then was tested under third-point loading. The measurements taken were tested using analysis of variance to determine if there was a significant difference due to reinforcements, and the means were compared to find the most applicable fabric. The beams broke unevenly under testing, showing that fabric has properties that could divert harmful forces away. The second set, being reinforced with smaller strips, outperformed the first, and was therefore the more successful implementation. An ANOVA test showed that there was a significant difference between the different methods of reinforcements, and that muslin had the highest mean measurement, making it the most applicable fabric. Muslin was shown to be the most effective reinforcement among the fabrics; denim was the next best alternative, and spandex being the least effective. Muslin was also shown to have a positive effect in reinforcing concrete. The implications of the study could lead to cheaper roads in the Philippines.
Lopez, AEC, Judi, DJF & Morales, JMD. (2012). “Different Textiles and Designs for Fabric Reinforced Concrete”. Research Paper. Philippine Science High School – Main Campus. APPROVAL SHEET
This research work entitled, “Different Textiles and Designs for Fabric Reinforced Concrete” by Alfonso Elias C. Lopez, Darren James F. Judi, and Justin Marius D. Morales,
presented to the Faculty of the Philippine Science High School – Main Campus in partial fulfillment of the requirements in Science and Technology Research 2, is hereby accepted.
Ana Victoria R. Lloren Research Adviser
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Lopez, AEC, Judi, DJF & Morales, JMD. (2012). “Different Textiles and Designs for Fabric Reinforced Concrete”. Research Paper. Philippine Science High School – Main Campus. ACKNOWLEDGEMENTS
We’d like to thank God for His guidance in our endeavors (most especially this one). It is Him who inspired us to carry on, and our burdens become ever lighter through His intervention. Ad Majorem Dei Gloriam; our work is for His greater glory. For providing us the means for our experimentation, we thank the DPWH North Manila Engineering District, DPWH Bureau of Research and Standards, and SolidMix Corporation. Their help and provisions of equipment allowed for quick and effective experimentation. We thank our parents, most especially Joan Morales, who helped us acquire our fabric, and Ruy Lopez, who helped arrange meetings with our, for lack of a more apt term, sponsors. We thank the teachers who have helped us bring this to fruition: our adviser Ma’am
Lloren, Sir Alcarez, and Sir Ayaay. They drove us to flesh out and complete this paper, which we would not have finished otherwise. Finally, we would like to thank STR as part of the curriculum. Research is an arduous process, and without this being a requirement, we would not have done it. Yet we become better than ourselves through these tasks. Almost ashamedly, we would like to thank that one unit on our grades.
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Lopez, AEC, Judi, DJF & Morales, JMD. (2012). “Different Textiles and Designs for Fabric Reinforced Concrete”. Research Paper. Philippine Science High School – Main Campus. TABLE OF CONTENTS
Page Approval Sheet..................................................................................... ..................................
i
Acknowledgements..............................................................................................................
ii
Table of Contents.................................................................................................................
iii
List of Tables.............................................................................. .........................................
V
List of Figures......................................................................................................................
vi
Introduction..........................................................................................................................
1
Background of the Study..........................................................................................
1
Statement of the Problem.........................................................................................
1
Significance of the Study..........................................................................................
2
Scope and Limitations..............................................................................................
2
Review of Related Literature...............................................................................................
4
Concrete...................................................................................................................
4
Concrete Testing.......................................................................................................
5
Third-Point Loading Test............................................................................
5
Concrete Reinforcement..........................................................................................
7
Reinforced Concrete....................................................................................
7
Fiber-Reinforced Concrete...........................................................................
8
Fabric.......................................................................................................................
8
Denim...........................................................................................................
9
Muslin..........................................................................................................
9 iii
Lopez, AEC, Judi, DJF & Morales, JMD. (2012). “Different Textiles and Designs for Fabric Reinforced Concrete”. Research Paper. Philippine Science High School – Main Campus. Spandex........................................................................................................
9
Materials and Methods.......................................................................................... ................ 10 Process Flowchart....................................................................................................
10
Creation of Setup....................................................................................................
11
Data Gathering........................................................................................................... 12 Data Processing......................................................................................................... 13 Results and Discussion................................... ....................................................................... 15 Creation of Setup....................................................................................................... 15 Data Gathering........................................................................................................... 16 Data Processing......................................................................................................... . 17 Summary and Conclusion....................................................................................................
23
Recommendations................................................................................................................
24
Bibliography........................................................................................................................
25
Appendix.............................................................................................................................
27
Moduli of Rupture and ANOVA Results.................................................................
27
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Lopez, AEC, Judi, DJF & Morales, JMD. (2012). “Different Textiles and Designs for Fabric Reinforced Concrete”. Research Paper. Philippine Science High School – Main Campus. LIST OF TABLES Table
Title
Page
1
Results and Modulus of Rupture for the first set of samples
18
2
Results and Modulus of Rupture for the second set of samples
19
3
Mean MORs for the first and second set-ups
21
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Lopez, AEC, Judi, DJF & Morales, JMD. (2012). “Different Textiles and Designs for Fabric Reinforced Concrete”. Research Paper. Philippine Science High School – Main Campus. LIST OF FIGURES Figure
Title
Page
1
The compression machine loaded with a sample from the first set
16
2
Uneven cracks formed in the first set of concrete beams
17
3
Strips of fabric can be seen where the samples cracked
20
4
Graph of mean MORs for all samples
21
vi
INTRODUCTION Background of the Study
Concrete, a mixture of cement, aggregate, and chemical additives (CCAA, 2004), is a vital element in structures such as buildings and bridges. As a material, concrete is known to have high compression strength. However, it lacks tensile strength, and therefore flexural strength, leaving it vulnerable to bending and stretching. This property is essential to roads and sidewalks, being constantly under stress require considerable flexural strength. Thus, concrete-producing companies have tried to find ways to augment the tensile strength of concrete. The usual approach is to reinforce concrete with steel reinforcement bars (also known as rebar) or wire mesh, giving it great flexural strength, but this approach is costly to employ extensively on large road and highway projects. To illustrate this point, a square section of sidewalk measuring 4.5 m at one side would require a 12 mm diameter wire mesh, spaced so that the empty spaces measure 30 cm x 15 cm. This equates to 202.5 m of wire, and at a price of 17.76 Php/m for structural steel wire (Capitol Steel), the mesh would cost 3600 Php. Another approach is to reinforce concrete with small fibers. Various materials have been tested for this application, such as steel, bamboo, wood pulp, and polystyrene, but these forms of reinforced concrete show little improvement in terms of tensile strength. Statement of the Problem
This research aimed to test the implementation of common textiles to reinforce concrete and to test if its flexural strength surpasses unreinforced concrete.
1
The research used spandex, denim and muslin fabrics in reinforcing concrete. These underwent stress tests, such as third-point loading tests, to measure flexural strength. The reinforced samples were tested to see if any of them perform significantly better than unreinforced concrete. The best configuration was recorded as well. The concrete used was controlled in the measure of Portland cement, aggregates, and additives. The method of mixing, curing, and finishing was also kept constant. The only change between samples were the presence, material, and design of reinforcement. The test results provided basis for conclusions. If there is at least one configuration that outperformed standard concrete, it would prove that reinforcement with common textiles is beneficial. The textiles were checked if they are less costly than other reinforcing materials. Significance of the Study
Extensive road projects and highways are frequently being built and maintained on a national scale. These public works are vital for transportation, and therefore key elements for travel, commerce, emergency situations, and other matters. This requires millions if not billions in government budgeting (Sun Star Bacolod, 2011), much of which is for the material cost of cement, aggregates, and reinforcement. While not all of the steel rebar can be replaced with fabric, a lot of roads can be reinforced with fabric instead of steel, as it should be enough reinforcement should fabric be a plausible material. Scope and Limitations
The study was concerned with the possibilities of fabric as reinforcements to concrete to improve flexural strength. No compression, impact or other tests were performed. 2
Only standard horizontal concrete (for use in roads) was used. No extra admixtures or other additives were used.
3
REVIEW OF RELATED LITERATURE Concrete
Concrete is an artificial material consisting mostly of water, cement and aggregate (coarse powder of a stony substance, such as gravel or sand) (CCAA, 2004). Having a solid, stony consistency, it is a common building material, for housing, infrastructure, and other constructions. The Philippines spends millions if not billions annually on concrete infrastructure (Sun Star Bacolod, 2011). Mixed concrete has a syrupy consistency with significant viscosity. This determines its workability (the capacity for the concrete to flow and be spread) (Camp, n.d.), which can be modified with an increase in water content or the presence of certain admixtures (plasticizers). Because of this, concrete is usually poured and shaped into the desired product and is kept in place with supporting surfaces or molds (West & Araya, 2009). The concrete then hardens through hydration, absorbing nearby water to incorporate into a mineral-like structure (Camp, n.d.). Concrete sets into a solid form within several hours and is left in a humid environment or submerged in water to cure (CCAA, 2004). The curing process allows hydration to continue, improving the strength of the concrete. Concrete requires 28 days to properly cure (Camp, n.d.), but this can be reduced to as little as 3 days with the addition of admixtures (namely, accelerants). The end result is a rigid, homogeneous construction, likely in the form of columns for foundations, walls, buildings, beams for bridges, and roads. Concrete, being a rigid, mineral-like material, posesses considerable compressive strength (CCAA, 2004). In practicality, this pertains to its ability to carry proportionally large amounts of weight without being crushed or fractured. This is the property that makes 4
concrete a viable material for use in tall buildings and other structures, where the lower portions must carry the weight of the upper portions. However concrete, like most rigid materials, has very little tensile strength. By rule of thumb, concrete only has 10 - 15% of their compressive strength in tensile strength (Camp, n.d.). This translates to a concrete rod being likely to break when pulled apart or bent. This makes it difficult to construct bridges, sidewalks and roads purely made of concrete, since these structures are constantly under a force that is concentrated only on small areas at a time, creating tension. Concrete Testing
Concrete, as a common building material, is usually subject to testing before use. Most tests are destructive (the sample is broken in the process and therefore cannot be used anymore), so the usual procedure is to take a sample of concrete to be used, and use that for the destructive tests. If the sample passes the tests, the rest of the batch is assumed to stay within standard as well. Concrete is shaped into cylinders for most compressive strength tests, into cubes for impact strength tests, and into rectangular beams for tensile strength tests. DPWH offices have the equipment and standards to run these tests. Construction works, especially public constructions are required to submit their concrete for testing. Third-Point Loading Test
The third-point loading test (NRMCA, 2000) is a standard test used by the DPWH for horizontal concrete, which are concrete used in roads and sidewalks. It is a flexural test; it determines the ability of rigid materials such as concrete to bend without breaking. 5
In this test, a sample of concrete is poured into a 6” x 6” x 21” beam. It is left to set
and cure according to the specified curing time of the mix. After curing, the beam is placed in a compression machine or equivalent (such as a universal testing machine). The beam is placed so that the bottom rests on evenly on two rollers spaced 18” apart. Pressure is applied
through a plate placed on top the middle third of the 18” between the rollers. The pressure gradually increases until the beam breaks. As long as the break is not further than 5% of the total length of the beam away from the middle third, or is within the middle third (however, this is unlikely), the test result is acceptable, otherwise it is discarded (University of New Mexico, n.d.). The result is interpreted into the Modulus of Rupture (MOR). It is determined as:
MR
Pa bd
2
(if the break is outside the middle third by less than 5% of the length of the beam)
MR
P bd
2
(if the break is within the middle third) MOR is the Modulus of Rupture, P is the peak pressure reached upon breaking, L is the length between the rollers, a is the length between the crack at the bottom and the nearer roller, b is the breadth or width of the beam, and d is the depth or height of the beam. The MOR is the value that represents the tensile strength of the beam. 6
Concrete Reinforcement
Concrete is a rigid material that can be set into any shape, and therefore can accommodate for additional physical reinforcement. Reinforcements are added to augment the compressive, tensile or impact strength of the concrete. Concrete, after all, is cement mixed with aggregate to take the physical properties of the aggregate, so other additions can be made without compromising the initial strength. Reinforced Concrete
Reinforced concrete (Pelger, 2010) refers to concrete augmented with steel rebar (short for “reinforcement bar”) or wire mesh made of steel or dense plastics. Rebar is laid
along the length of a concrete construction, while wire mesh is used parallel to a surface. Steel is much stronger than concrete in terms of tensile and compressive strength, but is less abundant and does not last as long without corrosion. The rebar (or wire mesh) is then emplaced right before pouring (CCAA, 2004) so that the rebar or mesh is inside the concrete when set. The steel is then less susceptible to corrosion, and the concrete takes on (in part) the strength of the steel. Steel rebar is produced in the Philippines, at Php 20.00 per kilogram (Captol Steel, n.d.). However, as reinforcement is usually extensive, the overall cost rises significantly. Steel mesh is usually imported, and is of a different standard; sidewalk sections which require mesh are 4.5 m long, while wire mesh produced overseas adheres to a standard length of 6.0 m, therefore creating 25% wastage. This reduces the desirability of wire mesh, even if it is required by current standards.
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Reinforced concrete is the most common method of improving concrete, and is standard in most constructions in the Philippines, barring most small housing (due to additional costs of reinforcement). Fiber-Reinforced Concrete
Fiber-Reinforced Concrete (FRC) is a form of reinforcement currently being studied. It relies on small fibers being mixed in with the concrete, in the form of small strands or loops (U.S. Patent No. 3616589, 1971). This forms bonds between several infinitesmal points in the concrete, strengthening it akin to wood pulp fibers bonding together to form paper. (Banthia, 2008) FRC can improve compressive strength, and is known to greatly improve impact strength (Maloney, 2005); a sample of FRC can take several strikes before cracks appear, and will not break apart easily with repeated strikes. FRC has been reviewed by the Department of Public Works and Highways Bureau of Research and Standards, and has found current implementations lacking; the increase in strength other than impact strength was not significant, and is too costly to employ. FRC is uncommon in use in the Philippines, where reinforced concrete is still mostly employed. Fabric
Fabric, or textile, is a thin material woven from fibrous strands of cotton, plastic or nearly any other fiber. Unlike concrete, fabrics are elastic materials, and are more susceptible to warping and stretching instead of breaking or fractures. This can lead to problems as fabrics can deform into other shapes permanently, and have less resistance to outside forces.
8
Fabrics are usually used in the form of cloth for clothing, decoration and upholstery. They are also used in artworks, filters and as support for composite materials such as fiberglass. Denim
Denim is a fabric made of thick cotton fibers in twill weave, which cause it to be characteristically rugged (Özdil, 2008). Denim is well known as the material for jeans, and is also used in jackets, pants, upholstery and overalls. Muslin
Muslin is a fabric of loosely woven cotton fibers, which cause it to be characteristically thin. Beth (2008) finds muslin to be “one of the most versatile and
inexpensive fabrics to use for a wide variety of different projects and applications”. Air and water pass easily through muslin, making it an ideal filter or medical gauze. It is also used for light clothing and sackcloth. Spandex
Spandex fabric is made with cotton and a polyurethane-polyurea copolymer. The addition of this polymer allows the fabric to be very elastic compared to other fabrics (IVC, 2010). Spandex has a greater tensile strength than rubber, generally twice as strong (AFMA, 2010). The fabric could be stretched up to seven times its length and expected to revert back almost to its original length. This elasticity provides greater comfort for the one wearing it. Because of this property, spandex is usually used in garters, underwear and compression garments. 9
MATERIALS AND METHODS Process Flowchart
10
Creation of Setup
Metal wire (laundry wire, 14 gauge) from a local hardware store was bent into 48 support structures that raise a 2.0 in. (5.0 cm) cylinder by 1.7 in. (4.4 cm). Their particular shape is assumed to be unimportant as long as they are generally uniform in shape and size. Fabric from a local open market was prepared for use; each of the fabrics (denim, muslin and spandex) was cut into three pieces of equal length (12.6 in. or 32 cm) and width (21 in. or 53 cm), making nine pieces total. These were the fabrics used for the first design. Another set of fabric was cut into 39.4 in. (100 cm) by 13.1 in. (33.3 cm) pieces, three each for the three fabrics. Each of these pieces was separated, and cut into approximately 1.0 in. (2.54 cm) by 2.0 in. (5.08 cm) strips, creating 9 sets of strips, three for every fabric. These were used for the second design. Concrete and molds (measuring 6.0 x 6.0 x 21in. or 15 x 15 x 53 cm) were acquired at the SolidMix batching plant. For the first design, the concrete was used to create the reinforcements: Each piece of fabric was laid out, and concrete poured along the length, for each piece. The pieces were then rolled into cylinders, containing the concrete inside. The cylinders are 21 in. (53 cm) long and 2.0 in. (5.0 cm) in diameter. There were three cylinders for each of the three fabrics, nine cylinders total. Four supports were placed inside each of the twelve molds. Each of the nine reinforcements was then placed in separate molds, leaving three without any reinforcement. 11
All the molds were filled with concrete. The concrete in the molds were left to dry overnight and then removed from the molds. The concrete beams were immediately submerged in water to be cured. The second design had twelve molds, filled with the same kind of concrete. However, in place of tubes of fabric supported by wire, the fabric strips were mixed in by hand as the concrete was poured into the mold. Each of the nine sets of fabric was placed in separate molds, with three more molds having only concrete as a control. The result was twenty-four concrete beams; three replicates of six treatments, each treatment being the fabric the beam was reinforced with along with its reinforcement design, and six beams for the control setups, three replicates with wire structures (for the first design), and three without (for the second). Data Gathering The beams were grouped by the reinforcement applied (denim, muslin, spandex, or none) and by reinforcement design (in fabric cylinders or strips). Each beam was tested with a third-point loading test: Each beam was placed horizontally in a compression machine (from the testing laboratory of DPWH North Manila), where the pressure was applied on the middle 6.0 in. (15 cm) of the top surface. The beam is held up only on two rollers, spaced 18 in. (46 cm) apart. These rollers are near the ends of the beam. Pressure was applied, and gradually increased until the beam fractured. The distance from the crack to the nearest edge was recorded, as well as the pressure reached upon breaking. These were used to calculate for the Modulus of
12
Rupture (MOR). Because all the beams broke within the middle third, the MOR is determined with the calculation:
MR
P 2
bd
Where P is the peak pressure reached upon breaking, L is the length between the rollers, b is the breadth or width of the beam, and d is the depth or height of the beam. The MOR is the output of the third-point loading test. Data Processing The Moduli of Rupture was tabulated, so that the moduli of each of the six treated groups can be compared against the moduli of of their corresponding control group. Onetailed T-tests (α 0.05) was used to check if any of the reinforced groups had significantly higher moduli than their control group. (H o: μcontrol μdenim and μcontrol μ muslin and μcontrol = μspandex, Ha: μ control < μdenim or μcontrol < μ muslin or μcontrol < μspandex) If more than one group had
significantly higher moduli, an ANOVA (or if there are only two, a two-tailed T-test, either having α 0.05) was used to check if any group has significantly higher moduli. (H o: μdenim = μmuslin μspandex, Ha: μdenim ≠ μmuslin ≠ μspandex).
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RESULTS AND DISCUSSION Creation of Setup
The wire-frame supports were bent out of galvanized iron (gauge 14) wire, and while not precisely consistent, had equal height (in the center, where it supports the cylindrical reinforcement) and width. Four supports were placed in every mold. The fabric did not wrap very easily around the concrete. They had to be dipped in wet concrete (by hand) to be rolled up to allow wet concrete to hold the shape of the fabric. As a result, implementation became more difficult, as prolonged skin contact with the concrete had irritating effects on the skin. This was due to the accelerant in the mix, which reduced curing time by accelerating the effects of hydration. This causes the wet concrete to leech water away from skin upon contact. Frequent washing and brief exposure time allowed the process to be continued. The second set proceeded more quickly as there was much less preparation required. The fabrics were cut into strips with scissors, and measured with a ruler. These strips were kept in separate containers, and during pouring, were added to their respective molds after these molds were mostly filled. They were then mixed in by hand, and the remaining space was filled with concrete. The concrete beams were poured and were given one week to cure (as prescribed in the concrete mix design) in a curing pond at DPWH North Manila. They were tested after exactly one week of curing.
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Data Gathering
One by one, the beams were placed inside a compression machine as seen in Figure 1, and underwent a third-point loading test. All the beams cracked in the middle third (which causes the calculation of the Modulus of Rupture (MOR) to account for the length of onethird of the tested section, instead of the length from the end to the crack) In the first set (the beams with wireframes and cylinders of fabric) , three reinforced beams (the second spandex beam, the first muslin beam, and the second denim beam) fractured unevenly, with the general plane of the cracking to be angled away from being perpendicular to the length. This could be an effect of the fabric reinforcement, diverting forces away from their original paths. Such a property could be beneficial as it can help dampen forms of mechanical shock. Finally, it was noted that the inclusion of fabric prevented the cracks created to widen.
Figure 1: The compression machine loaded with a sample from the first set.
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Figure 2: Uneven cracks formed in the first set of concrete beams.
As stated above and seen in Figure 2, all of the beams cracked in the middle one-third section, causing them all to have the same length value. All the beams meet the minimum standard of DPWH (that they withstand at least 3.82 MPa of pressure), so the mix of the concrete is shown to be strong enough for regular use. The calculation of MOR was done by multiplying the pressure by thrice the length 0.1524 m (length from the end to the middle third), and dividing by 5.486 m 3 (in the MOR equation, berth by depth squared, all with the standard length 15.24cm). Hence, the unit of measurement is in MPa per square meter. Data Processing
The MOR of the first set of samples is shown in Table 1. The highest MOR recorded of 20.32 Pa/m2 is actually from the unreinforced beams (the control), and the lowest recorded 16
of 14.05 Pa/m2 are from the muslin and spandex beams. The data shows that the addition of reinforcement may have been detrimental instead of beneficial. This may be due to the fabric interfering with the bonding of the cement, effectively creating a hollow area in the center of the interconnecting bonds, reducing the tensile strength. Table 1: Results and Modulus of Rupture for the first set of samples. Type of Reinforcement
Denim
Muslin
Spandex
Control
Control No.
Peak Pressure (Pa)
Length to crack (m)
MOR (Pa/m^2)
1
5.43
0.1524
17.81
2
5.43
0.1524
17.81
3
4.67
0.1524
15.30
1
5.05
0.1524
16.56
2
4.67
0.1524
15.30
3
4.28
0.1524
14.05
1
4.28
0.1524
14.05
2
4.29
0.1524
14.08
3
4.67
0.1524
15.30
1
5.43
0.1524
17.81
2
6.20
0.1524
20.32
3
5.43
0.1524
17.81
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Table 2: Results and Modulus of Rupture for the second set of samples. Type of Reinforcement
Denim
Muslin
Control No.
Actual Load (kN)
Peak Pressure (Pa)
1
45
5.81
0.1524
19.07
2
60
7.75
0.1524
25.42
3
54
6.98
0.1524
22.88
1
63
8.14
0.1524
26.70
2
Spandex
Control
N/A
N/A
Length to crack (m)
N/A
MOR (Pa/m^2)
N/A
3
57
7.36
0.1524
24.15
1
45
5.81
0.1524
19.07
2
48
6.20
0.1524
20.34
3
57
7.36
0.1524
24.15
1
54
6.98
0.1524
22.88
2
54
6.98
0.1524
22.88
3
54
6.98
0.1524
22.88
The reinforced beams of the second set (the beams with fabric strips) had higher moduli than those of the first. As seen in Table 1, the first set had a range from a minimum of 14.05 Pa/m2 to a maximum of 20.32 Pa/m 2, while in Table 2, the second set ranged from 19.07 Pa/m2 to 26.70 Pa/m2 ,excluding the second muslin beam, which did not provide data due to mechanical failure of the dial of the compression machine. It was assumed, however, that the second muslin beam would have a similar value as it generally broke at a similar strength between 7.36 Pa and 8.14 Pa. Furthermore, the pattern of its breaking was also
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consistent. These beams did not have uneven breaking, but they were shown to break where some of the strips were interspersed, shown in Figure 3.
Figure 3: Strips of fabric can be seen where the samples cracked
The improvement in the second set may be due to the chemical properties of fabric to bond as opposed to its physical properties to resist forces. This might explain how a smallerscale implementation may be more effective due to increased surface area. To compare the relative strengths of each treatment, the means of the MORs of each treatment, shown in Table 3, along with their respective controls, were compared directly to rank the flexural strength. In both sets, the control proved to be stronger than most; only the muslin treatment of the second set had a mean higher than its respective control, as seen in Figure 4.
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Table 3. Mean MORs in
Set-up
Pa/m2 for the first and second set-ups. Denim
Muslin
Spandex
Control
1
16.95
15.25
14.41
18.64
2
22.46
25.42
21.19
22.88
Figure 4: Graph of mean MORs for all samples.
The MORs of the reinforced beams were then inputted into two analysis of variance (ANOVA) tests: one for the first set and one of the second. The ANOVA test used was a one-tailed test (α 0.05) to determine if the reinforced samples had significantly higher MORs than those of their respective control. The hypotheses are: Ho: μcontrol μdenim μmuslin μspandex Ha: μcontrol ≠ μdenim ≠ μmuslin ≠ μspandex
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The ANOVA test accounted for the missing data for the second muslin beam, which cannot be measured, as mentioned beforehand. The ANOVA test was tailored around it by changing the degrees of freedom used. The ANOVA test had a score of 5.43, which is above the critical value of 2.95. The ANOVA tests show that there is significant difference between the means of the groups' MOR. Certain factors may have affected the results. Although the fabric strips were mixed randomly into the concrete sample, thoroughness in the mixing may not have been ensured as the workability of the concrete was kept on minimum. Also, because the concrete was mixed in three batches per set, there might be slight differences in the actual mix. Finally, there is a maximum difference of one hour in the concrete being transferred to a curing pond as the first samples of each set were left out that much longer. However, these sources of error are likely not significant enough to have changed the conclusion. Since the only treatment with a mean higher than its respective control was muslin, it was assumed that muslin was the most applicable fabric for reinforcing concrete. Spandex, having the lowest means in both sets, is the least applicable, leaving denim between the two.
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SUMMARY AND CONCLUSION
Of the three fabrics used (denim, muslin and spandex), muslin is most-suited for use in reinforcement of horizontal concrete to improve its flexural strength, in the form of mixing in small pieces of muslin in with the concrete. Such reinforcement allows it to have a higher breaking point under tension, which would allow it to last longer. The improvement is significant, as checked with an Analysis of Variance test, showing that the differences between the muslin beams against other beams is greater than (and therefore more significant than) the differences between each muslin beam. Reinforcing concrete with muslin is slightly less costly than the doing the same with steel rebar. The muslin in one beam cost 25 Php (75 Php/m 2 x one-third of a square meter in each beam). The equivalent in rebar (2 bars of 12mm steel rebar, 53.34 cm long, along with 3 bars of 12mm rebar, 15.24 cm long) would cost about 27 Php. This is an 8% difference in cost (2/26 * 100%), which is substantial. The wastage that is inherent to using wire mesh (wire mesh must be cut to size, and the excess is unusable) is not present in muslin, hence increasing the difference of costs. It cannot be concluded if any of the fabrics is more cost-effective than concrete, as such was not tested, but it can be concluded that among the fabrics, muslin is less costly and an effective alternative to steel rebar in reinforcing horizontal concrete.
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RECOMMENDATIONS
It is recommended to continue testing for the 28 and 56-day strengths of fabricreinforced concrete, as the fabrics may degrade over time, causing a change to its effectiveness as reinforcement. A change in implementation is also recommended; even smaller pieces or individual fibers may be more effective.
23
BIBLIOGRAPHY
American Fiber Manufacturers Association, Fiber Economics Bureau (2010). Spandex Fiber. Retrieved from http://www.afma.org/f-tutor/spandex.htm Banthia, N. (2008, November). Fiber reinforced concrete. Paper presented at Advances in concrete technologies in the middle east conference, Dubai, UAE.
Beth,
N.
(2008).
Muslin
Fabric
and
Its
Many
Uses.
Retrieved
from
http://www.associatedcontent.com/article/1267647/muslin_fabric_and_its_many_use s.html?cat=24 Budget office allots P35M for road maintenance. (2011, September 1). Sun Star Bacolod . Retrieved
from
http://www.sunstar.com.ph/bacolod/business/2011/09/01/budget-
office-allots-p35m-road-maintenance-176771 Camp, C. (n.d.). Properties of concrete. Department of Civil Engineering, University of Memphis,
Memphis,
Tennesee.
Retrieved
from
http://www.ce.memphis.edu/1101/notes/concrete/section_3_properties.html Capitol
Steel.
(n.d.)
Capitol
Steel
Price
List .
Retrieved
from
http://www.capitolsteel.com.ph/pricelist.html. CCAA. (2004). Concrete basics - a guide to concrete practice. Australia: Cement Concrete & Aggregates Australia. Flexural strength of concrete - ASTM C78 (n.d.). Civil Engineering Department, University of
New
Mexico,
Albuquerque,
New
Mexico.
Retrieved
from
http://civilx.unm.edu/laboratories_ss/pcc/flexural.htm
24
Industrievereinigung Chemiefaser e.V. (2010). Elastane fibres (Spandex fibres). Retrieved from http://www.ivc-ev.de/live/index.php?page_id=73 Maloney, M. (2005). Structural Synthetic Fibres for Precast and Slab-on-Grade Construction. Construction Canada. NRMCA. (2000). Flexural strength concrete. Concrete in Practice, 16, Retrieved from http://www.nrmca.org/aboutconcrete/cips/16p.pdf Özdil, N. (2008). Stretch and bagging properties of denim fabrics containing different rates of elastane. FIBRES & TEXTILES in Eastern Europe, 16(1), 63-67. Pelger,
N.
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Concrete
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http://www.constructionknowledge.net/concrete/concrete_basics.php West, M., & Araya, R. (2009). fabric formwork for concrete structures and architecture. Proceedings of the International conference on textile composites and inflatable structures - structural membranes. 2009 Barcelona: CIMNE.
25
APPENDIX A
MODULI OF RUPTURE AND ANOVA RESULTS
Type of Reinforcement
Control No. 1 2 3 1 2 3 1 2 3 1 2 3
Denim
Muslin
Spandex
None
Denim x1
MOR 17.80
x2
Actual Load (kN) 42 42 36 39 36 33 33 33 36 42 48 42
Peak Pressure (Pa) 5.43 5.43 4.65 5.04 4.65 4.26 4.26 4.26 4.65 5.43 6.20 5.43
Muslin x
2
Length to crack (m) 0.1524 0.1524 0.1524 0.1524 0.1524 0.1524 0.1524 0.1524 0.1524 0.1524 0.1524 0.1524
MOR (Pa/m^2) 17.80 17.80 15.25 16.53 15.25 13.98 13.98 13.98 15.25 17.80 20.34 17.80
Spandex 2
None 2
2
316.75
MOR 16.53
x 273.11
MOR 13.98
x 195.54
MOR 17.80
x 316.75
17.80
316.75
15.25
232.71
13.98
195.54
20.34
413.71
x3
15.25
232.71
13.98
195.54
15.25
232.71
17.80
316.75
Total
50.85
866.20
45.76
701.37
43.22
623.79
55.93
1047.20
n X
3
3
16.95
15.25
Grand T(x) Grand 2 T(x )
14.41
3 18.64
195.77 3,238.56
Grand N
(Grand T ^ 2)/N Grand T(x^2) Grand(T^2)/n
3
12.00
3193.85 3238.56 3225.63
SS(bet) SS(w/in) SS(tot)
31.7823 12.9284 44.7107
26
