2.1 Materials
The materials used in the research process were cement, fine aggregate and coarse aggregate, three types of gabions (welded wire mesh, hexagonal wire mesh and expanded metal wire mesh) reinforcement bar, super plasticizer admixture and potable water.
The properties of the row materials have been duly investigated and the general properties are as clearly stated below
A. Cement, Admixture, and Water
The chemical reaction associated with the decarbonation of limestone at high temperature, which produces cement, releases a substantial amount of carbon dioxide. Cement is utilized in the design of concrete.(Khokhar et al., 2010). The cement used in this work was Ordinary Portland Cement which satisfies the standard of the building codes of Ethiopia.
In which its specific gravity is 3.15, Standard consistency = 34%, Initial setting time = 40mins
An admixture known as superplasticizer with a proportion of 0.2% was used in order to facilitate the strength-gaining period of the concrete.
Potable water readily available in the local area was used which satisfies the drinking standard of Ethiopia.
B. Fine aggregate(sand)
River sand readily available which satisfies the requirement to be used in concrete casting was used. The properties of the sand used were studied in the laboratory and are presented in the tables below. Lightweight sand provides the same tensile strength as natural sand but lowers the compressive strength of Ferro-cement specimens(SHAH SP and KEY, 1972; Batra
et al., 2017).
1. Gradation of the sand
The sand used in the research was tested for its basic properties. The laboratory tests made in the sand (fine aggregate) are sieve analysis, specific gravity, and silt content tests.
The majority of the sand used was passed through a 4.75 mm sieve. The gradation test result shows that the sand is well-graded sand with a fineness modulus of
Table 3
− 1 Sieve analysis (gradation results) of sand
Sieve size in mm |
Weight of sieve (gm) |
Weight of sand + retained sand(gm) |
Mass retained |
Percent retained (%) |
Cumulative percent retained (%) |
Percentage passing |
4.75 |
449 |
494 |
45 |
2.25 |
2.25 |
97.75 |
2.36 |
442 |
507 |
110 |
5.5 |
7.75 |
92.25 |
1.18 |
493 |
660 |
167 |
8.35 |
16.1 |
83.9 |
0.6 |
397 |
1282 |
885 |
44.25 |
60.35 |
38.65 |
0.3 |
362 |
978 |
616 |
30.8 |
91.15 |
8.85 |
0.15 |
341 |
498 |
157 |
7.85 |
99 |
1 |
Pan |
363 |
381 |
19.9 |
1 |
100 |
0 |
As the chart in Fig. 1 above shows the gradation of the sand used in the research is well graded.
2. Silt content of the sand
Since the presence of more silt or organic matter made concrete or mortar decrease the bond between the materials to be bound together and hence the strength of the mixture. The finer particles do not only decrease the strength but also the quality of mixture produced resulting in fast deterioration. Therefor it is necessary that one make a test on the silt content and checking against permissible limits.
Table 3
− 2 Silt content of the sand used
Sample number |
Amount of silt deposit above the sand (A) |
Amount of clean sand(B) |
Silt content= (A/B)*100% |
1 |
1mm |
46.5 |
2.15% |
2 |
1.5 |
48 |
3.13% |
3 |
1.2 |
48.5 |
2.06% |
Average silt content |
2.45% |
According to the Ethiopian Building Code Standard, if the silt content of the sand is more than 6% it shall not be used for construction. But the result (2.45%< 6%) complies with the standard and we used the sand material.
3. Specific gravity and water absorption of the sand
The main objective of the laboratory test is to determine the specific gravity and the water absorption capacity of the sand for use. The test has been made according to ASTM-C- 128 − 97 manual. Though the aggregates and sand we used were from a construction site on the main campus it has been found that duly studying the behavior of the materials is an important stage since it affects the final output of the concrete cast by the materials.
Table 3
3 Specific gravity and water absorption of the sand according ASTM-C- 128 − 97
Number |
Trial number |
1 |
2 |
3 |
Average |
1 |
Weight of oven dry specimen in air, in gm (A) |
458 |
452 |
464 |
|
2 |
Weight of pycnometer filled with water, gm (B) |
657 |
657 |
657 |
|
3 |
Weight of with specimen and water to the calibration mark, gm (C) |
934 |
940 |
949 |
|
4 |
Weight of saturated surface dry specimen, gm (S) |
500 |
500 |
500 |
|
5 |
Bulk specific gravity = A/(B + S-C) |
2.05 |
2.083 |
2.23 |
2.12 |
6 |
Bulk specific gravity (SSD) = S/((B + S-C) |
2.24 |
2.30 |
2.40 |
2.31 |
7 |
Apparent specific gravity = A/(B + A-C) |
2.53 |
2.67 |
2.70 |
2.63 |
8 |
Absorption capacity= [(S-A)/A] *100 |
9.1 |
10.62 |
7.76 |
9.1 |
C. Coarse aggregate
The aggregate that has used in the research had been examined for the fulfillment of ASTM-C-136-01 sieve analysis results and ASTM-C-127-88 standard test results for specific gravity determination.
1. Gradation of the coarse aggregate
Since the main intention of this research is to add aggregate for Ferro cement structures examining the gradation of the aggregate to be used is important. As a result, the sieve analysis results of the aggregate show.
An aggregate with the properties specified below was used. The aggregate has a maximum size of 14mm and most of the aggregate is retained in the 5mm sieve. Since some codes recommend not using materials that are finer than 5 mm as aggregate a sieving process has been made before casting the concrete.
Table 3
4 Sieve analysis (gradation test) result of the aggregate ASTM-C-136-01
Sieve size in mm |
Weight of sieve (gm) |
Weight of sand + retained sand(gm) |
Mass retained (gm) |
Percent retained (%) |
Cumulative percent retained (%) |
Percentage passing |
28 |
0.761 |
0.761 |
0 |
0 |
0 |
100 |
14 |
1.357 |
1.468 |
111 |
2.22 |
2.22 |
97.78 |
10 |
1.328 |
1.612 |
324 |
6.48 |
8.70 |
91.30 |
6.3 |
0.728 |
3.7 |
2972 |
59.44 |
68.14 |
31.86 |
5 |
0.712 |
1.247 |
535 |
10.7 |
78.84 |
21.16 |
Pan |
0.759 |
1.854 |
1058 |
21.16 |
100 |
0 |
2. Density of the aggregate
Table 3
5 Dry density of the aggregate used
Trial no |
Wight of the mold in Kg (A) |
Wight of the mold + filled aggregate in Kg (B) |
Wight of the retained aggregate ( C )= (B-A) |
Volume of the mold(m3) (D)=\(A=\pi {r}^{2}h\) d/2 = r = 0.08m, h = 0.16m |
Density in (Kg/m3) =(C/D) |
1 |
2.968 |
4.845 |
1.877 |
3.21536*103 |
583.76 |
2 |
2.968 |
4.907 |
1.939 |
3.21536*103 |
603.04 |
3 |
2.968 |
4.898 |
1.930 |
3.21536*103 |
600.24 |
Average density |
595.68 |
As the result in the above table reveals the aggregate, we used to be categorized into lightweight aggregates.
The reason why we need to determine the dry density of the coarse aggregate is that it is important to have the dry density in order to make the mix design calculations as well as to decide the compressive strength of the final cast concrete and as Ferro cement is a lightweight structure, we wanted to improve the material by lightweight aggregate in order to make it light as much as possible.
To go over all the other density (specific) gravity parameters this is also important.
3. Specific gravity and water absorption capacity of course aggregate ASTM-C-127-88
The specific gravity may be expressed as bulk specific gravity, bulk specific gravity (saturated surface dry (SSD) or apparent specific gravity. Those parameters are used to determine the volume requirements and in determining the mix ratio calculations based on mass.
Table 3
6 Specific gravity and water absorption capacity of course aggregate ASTM-C-127-88
Trial no |
Wt. of oven dry sample(gm) |
Wt. of saturated surface dry sample(B) (gm) |
Wt. of saturated surface dry in water(C) (gm) |
Bulk specific gravity A/(B-C) |
Bulk specific gravity (SSD) B/(B-C) |
Apparent specific gravity A/(A-C) |
Water absorption capacity in% |
1 |
989 |
1000 |
548.3 |
2.19 |
2.21 |
2.24 |
1.1 |
2 |
990 |
1000 |
554.1 |
2.22 |
2.24 |
2.27 |
1 |
3 |
989 |
1000 |
555.5 |
2.22 |
2.25 |
2.28 |
1.1 |
Average values |
2.21 |
2.23 |
2.26 |
1.07 |
D. Gabion (different steel wire meshes)
Gabion (steel wire) meshes are thin steel wires has served in many fields of real-life applications though in different orientations and different mechanisms of applications. Most of the applications of gabion include that uses as a fence, uses in soil and water conservation works to prevent excessive erosion, and in some developed societies as building decoration works as well. The materials have very flexible behavior to be used in making different forms of ornamental works like different shapes in places where people used to recreate.
Different types of meshes are available almost in every country in the world. Two important reinforcing parameters are commonly used in characterizing Ferro cement and are defined as the volume fraction of reinforcement; it is the total volume of reinforcement per unit volume of Ferro cement. The specific surface of the reinforcement is the total bonded area of reinforcement per unit volume of the composite. The principal types of wire mesh currently being used in this research are hexagonal (chicken) wire mesh welded square wire mesh and expanded metal mesh among the available steel wire meshes. The addition of wire mesh layers as reinforcement improves flexural strength, cracking behavior, and energy absorption capability greatly. (10)
1. Hexagonal or chicken wire mesh
This mesh is readily available in most countries, and it is known to be the cheapest and easiest to handle. The mesh is fabricated from cold drawn wire which is generally woven into hexagonal patterns. Special patterns may include hexagonal mesh with longitudinal wires. The chicken wire mesh used in this research has a thickness of 2.2mm and opening spacing of 35mm. The yield strength of the steel wire mesh is considered as 450Mpa as taken from the manufacturer’s specifications.
2. Welded square wire mesh
In this mesh, a grid pattern is formed by welding the perpendicular intersecting wires at their intersection. This mesh may have the advantage of easy molding into the required shape; it has the disadvantage of the possibility of weak spots at the intersection of wires resulting from inadequate welding during the manufacture of the mesh. Welded square wire mesh with a thickness of 0.7mm was used during the research.
3. Expanded metal mesh
This mesh is formed by cutting a thin sheet of expanded metal to produce diamond shape openings. It is not as strong as woven mesh, but on cost to strength ratio, expanded metal has the advantage. This type of mesh reinforcement provides good impact resistance and crack control, but they are difficult to use in construction involving sharps curves.
Sharma, (2016) Recommended that the design strength for the mesh reinforcement shall be based on the yield strength fy of the reinforcement but shall not exceed 690 N/mm2. Design yield strengths of various mesh reinforcements are shown in the table below as per the data from the material manufacturers and recommendations of(Sharma, 2016). These shall be used for design only when test data are not available. In the research, we used this data for qualitative comparisons of the results got from the laboratory tests.
Table:3–7 Minimum Values of Yield Strength and Effective Modulus for Steel Meshes and Bars Recommended for Design
|
Welded Square Wire Mesh |
Hexagonal Mesh |
Expanded Metal Mesh |
Longitudinal Bars |
Yield Strength |
fy N/mm2 |
310 |
450 |
310 |
300 |
Effective Modulus |
(Er) Long.(N/mm2) |
104000 |
200000 |
138000 |
200000 |
(Er) Trans. (N/mm2) |
69000 |
200000 |
69000 |
---- |
3.2 Mix design
The chemical composition of the cement, the nature of the fine aggregate (sand), coarse aggregate and the water-cement ratio are the major parameters governing the properties of the concrete. The concrete matrix is designed for its appropriate strength and maximum denseness and impermeability, with sufficient workability to minimize voids and to avoid map cracking. Cement mortar used in ferro concrete acts as a good insulator and the reinforcing wire mesh can reduce surface upheaval better than plain concrete (Greepala and Nimityongskul, 2008). Precautions are necessary to maintain the small cover and in the selection of aggregates, mixing, placing, and curing (Sakthivel and Jagannathan, 2011). Mortar recommended for Ferro cement shall comprise particles or aggregates of limited size. The mortar matrix usually comprises more than 95 percent of the Ferro cement volume and has a great influence on the behavior of the final product. The cement mortar should be mixed with a proper sand-cement ratio (ranging from 1.5-2.5 by weight) and water-cement ratio (between 0.35-0.45 by weight) in order to achieve sufficient plasticity and facilitate easy casting. Many defects are possible due to a lack of complete infiltration and consolidation.
The ingredients used for mixing concrete should be carefully batched by weight, including the water, and added or charged in the mixer so that there is no caking. The water cement ratio should be as low as possible but the sand-cement ratio should be adjusted to provide a fluid mix for initial penetration of the armature followed by a stiffer, more heavily sanded mix at the finish(Sakthivel and Jagannathan, 2011). For most applications with normal weight concrete and steel meshes, the 28-day compressive strength of 150 X 150 mm moist cured cube should be not less than 35MPa. According to the recommendations for ferroconcrete, we have used a water-cement ratio of 0.4 and a material proportion of 1:1.5:2 (cement, sand, and coarse aggregate respectively to cast a concrete of grade more than 35 Mpa. Since the concrete material is expected to possess good strength in a small thickness, the result is considered as ferro cement material improved by the addition of coarse aggregate of maximum size 14 mm taking in to account the opening of the gabion. Normally the slump of fresh concrete we cast was a true slump with 37mm as shown in Fig. 3.6 above. Admixtures or additives have been added to improve the performance and workability of the concrete.
3.3 Mold Fabrication
Due to the lack of readily available standard molds in the laboratory temporary molds were prepared for the flexural specimens and for the energy absorption test specimens. The molds were prepared in such a way that the dimension of the inner mold satisfies the requirement of the standard molds. Two types of molds were prepared with inner dimensions of L: W: D= (500:100:100) in mm for flexural mold and the second type slabs for energy absorption test with inner dimensions L: W: D = 400mm:300mm:75mm, by considering the two-way aspect ratio and the deep beam effect which shall be greater than 4 to avoid deep beam effect.
3.4 Experimental Plans
3.4.1 Flexural Tests
A. Flexural Specimen Preparation
Flexural test gives another way of estimation for the tensile strength of concrete. Many heterogeneous aggregate materials, such as rocks, concretes, and certain ceramics, as well as some metals, have improved fracture resistance due to a toughening mechanism caused by the shielding of the crack tip by a nonlinear zone of dispersed microcracking or void formation(Bazant and Kazemi, 1990).
The application of ferrocement cover raises the ultimate flexural stress and the first fracture load somewhat. The percentage of mesh reinforcement and the thickness of the ferrocement layer increased the first fracture load. For specimens with a ferrocement coating, there was a significant reduction in crack width and spacing (64–84%)(Al-Kubaisy and Materials, 2000).
In this research, a total of 45 prisms with a total dimension of (width = 100mm*depth = 100mm*length = 500mm) was casted in a readily made mold. Casting process of the model specimens was done in a special mold prepared from timber due to the absence of enough molds in the laboratory. The flexural test specimens were made up of three different types of gabion reinforcements used in four different set ups. The sample specimens of different wire mesh reinforced concrete models with different is shown in Figs. 3.8, 3.9, and 3.10 below.
B. Testing of specimens
The testing was made in a universal compression machine with ultimate loading capacity of 1000 kN.
3.4.2 Compressive strength tests
The compressive strength and energy absorbed rose with increasing loading rate, indicating that they were nearing a constant value(Atchley, 1967).
A. Specimen preparation
A total of 33 compressive specimens have been prepared for 11 different specimens. A prepared layers of each mesh type according to the number of layers required to the test was prepared and casting of the specimens was made in a standard 150mm*150mm*150mm cubes readily available in the laboratory. The casting was done by first placing the wire meshes inside the cube by providing the necessary concrete covers as illustrated in the figures below.
The specimens then were allowed to cure for 14 days to attain the maximum strength hence admixture was used. During the specimen preparation due to the interruptions in the power the compaction was made using tamping rod and hand mixes was also used.
B. Testing of the different cube specimens
The testing of the specimens was made in a compressive machine.
3.3.3 Energy absorption test
The crack-arresting mechanism of such composites is improved by the uniform distribution and high surface area-to-volume ratio of the reinforcement (wire mesh)(Kaish et al., 2018). The wire mesh deformation and failure absorbed more than 80% of the impactor's kinetic energy, while frictional energy dissipation only accounted for roughly 10% of impact energy(Wang et al., 2021).
A. specimen preparation
A total of 45 specimens have been prepared for energy absorption tests in which the details of the specimen types. To prepare the different specimens a temporary form work of dimensions 400mm*300mm*75mm (length, width and thickness) respectively was prepared. Slabs reinforced by different types of mesh and with different number of layers were casted and cured for 14 days. The specimens were prepared as simply supported slab and a 3.028kg cylindrical steel alloy is allowed to fall freely from a 1.0m height on the top of the slab specimen. The number of blows was recorded at the instant where first crack was observed and at ultimate failure (total collapse of the structure) as figure 3.15.