Influence of Untreated Abaca Fibre on Mechanical Properties of Lightweight Foamed Concrete

One of the fundamental components of concrete is cement. It has been used as a binder in concrete, mortar, and other construction material. Concrete is made up by mixing the cement with fine aggregate and other admixtures such as AF until a hardening paste is formed. Cement is usually made from a chemical mixture such as silica, calcium, and other minerals. Cement is an important material with cohesive and adhesive properties capable of producing utterly compact mixing particles. The cement was purchased under the brand of “Castle” which fulfils the requirements stated in BS 196 [27]. The cement used in this research is Type 1. Type I is a general-purpose portland cement suitable for all applications where the special properties of other types are not necessary. It is used where cement or concrete is not subject to specific exposures, such as sulfate attack from soil or water, or to an objectionable temperature rise due to heat generated by hydration.

Fine aggregate is generally natural sand. The fine aggregate needs to pass a 9.5 mm sieve, while the required size of fine aggregate should be not exceeded 2 mm to achieve the desired properties of LFC as per the BS 882 [28] recommendations. Regarding this matter, this research utilized fine aggregate with a fineness modulus of 1.4 and a specific gravity of 2.7 as a constituent material in mortar mixes. After the fine aggregate was sieved, they were kept in a clean container until they were set to be mixed.

Generally, clean tap water was used in the mixture. However, if the water contains any chemical compounds, the efficiency of cement and aggregate can be affected. To ensure that an LFC possesses the required strength, durability and efficiency, an appropriate amount of water needs to be considered; during the mix, the hydration process will trigger the chemical bonding of cementitious content. An appropriate value of water is determined by the cement used in the mix. This research used the water-cement ratio of 0.45 since it will achieve the desired workability.

The protein-based surfactant (Noraite PA1) was chosen due to its high efficiency, potency, and dense cell bubble structure. This foaming agent capacity must determine using ASTM C869-91 [29] and ASTM C796 [30] for the test procedure. The production of foam uses a generator which is Portafoam PA-1. This machine is supplied with a digital timer that allows setting the flow rate acts where it converts the liquid chemical into foam. The Noraite PA1 can generate stable foam with a density of 55–70 kg/litre. This mixture can create 30 litres of foam.

Abaca is often disposed of with other agricultural wastes. The usage of AF in concrete can produce a clean, environmentally friendly, and reasonable price housing system in Malaysia. Thus, agricultural wastes can be used in place of or in addition to conventional construction material. The AF (plant of the family Musaceae) used in this research was supplied by DRN Technologies Sdn Bhd. This research is using various percentages of AF (0.15%, 0.3%, 0.45% and 0.6%) as an admixture in LFC. Fig. 1 shows the raw AF was weighed before mixing with the LFC base mix.

Figure 1

Tables 1, 2 and 3 demonstrate the chemical composition, physical attributes and mechanical properties of AF correspondingly. AF had superior cellulose proportion which may support considerably when in composite action with LFC cement matrix. Natural fibres with superior cellulose substance, usually, exhibit a low deformation with an excellent modulus of elasticity [31] and this is verified by the experimental data accomplished in their study. Moreover, it was testified that generally, the modulus of elasticity and tensile strength of plant fibre rises with a rising cellulose substance of AF.

To conduct the experiment in the current study, a total of 5 mixes were prepared. Table 4 shows the mixture design proportions of 550 kg/m³ density. It is crucial to remember that AF was used as an additive at concentrations ranging from 0.15%, 0.30%,0.45% and 0.60% by weight of the total mix in this analysis. As previously stated, the mortar was composed of cement, sand, and water in a ratio of 1:1.5:0.45.

Properly cured LFC has better surface hardness and can better withstand surface wear and abrasion. Curing also makes LFC more impermeable, which prevents moisture and water-borne chemicals from entering the LFC, thereby increasing durability and service life. It is essential to understand that a reduced amount of water in LFC will result in volatile temperatures. This will lead to a crack on the surface of LFC. After the specimens are demoulded, they were placed in a plastic wrap and securely tied and splashed with water to maintain the moist condition (Fig. 2). Following that, each of the specimens were removed from the plastic wrap on each testing day (day-7, day-28 and day-56) and ready for testing. Meanwhile, the specimens were dried for 24 hours at 100±5°C in the oven and then ready for compression, flexural and splitting tensile strength tests.

Figure 2

This test was performed using a GT-7001-BS300 universal testing machine with a 300 kN size as shown in Fig. 3. This test follows BS 12390-3 [32] using a cubic sample of 100 mm × 100 mm × 100 mm in size. Meanwhile, the axial compressive load acted on specimens at a rate of 0.2 N/sec before the failure occurred. The result was obtained, and the test was conducted on day-7, day-28 and day-56. The average compressive strength is determined using the 3 specimens. The calculation of compressive strength is as follows: (1) Compressive strength=breaking loadarea {\rm{Compressive}}\,{\rm{strength}} = {{{\rm{breaking}}\,{\rm{load}}} \over {{\rm{area}}}}

Figure 3

In this research, a rectangular beam of 100 mm x 100 mm x 500 mm was used to establish the LFC flexural strength shown in Fig. 4. The test was carried out according to BS EN 12390-5 [33]. The machine that aided in this test program is Go-Tech GT-7001-C10 which is a universal testing machine. The support's nominal distance was 300 mm, and the roller is let for free horizontal movement. The LFC has applied a constant load of 0.2 N/sec. The result was obtained, and the tests were conducted on the 7^th, 28^th and 56^th. The average flexural strength is determined using three specimens. The flexural strength is determined using the equation as below: (2) σf=3PL2bd2 \sigma {\rm{f}} = {{3{\rm{PL}}} \over {2{\rm{b}}{{\rm{d}}^2}}} where,

F – flexural strength

Figure 4

This test aims to ascertain the load under which LFC begins to fail. It is a phenomenon known as tensile collapse. This test is using BS EN 12390-6 [34] as a guide. The setup of splitting tensile strength is shown in Fig. 5. The diameter and height of the specimens are 100 mm and 200 mm, respectively. The machine that is used is GOTECH GT 7001-BS300 which is a universal testing machine. The specimens are subjected to 0.2 N/sec before the result was obtained. The test was conducted on the 7^th, 28^th and 56^th. The average flexural strength is determined using three specimens. Splitting tensile strength is determined using the equation as follows: (3) T=2PπLD {\rm{T}} = {{2{\rm{P}}} \over {\pi {\rm{LD}}}} where,

T – splitting tensile strength

Figure 5

Table 5 summarized the details of the LFC specimens, types of tests, the number of specimens and standard codes referred to in these mechanical properties tests.

A compressive strength test was conducted in this research to identify the ability of LFC to resist the load that is applied to it. This test can determine the performance of mechanical properties of the LFC according to ASTM C39. Fig. 6 below depicts the result of compression strength of LFC with a density of 550 kg/m³. The results show an increasing trend from day-7 until day-56 with AF in the LFC. When 0.15% AF was added to LFC, the growth rate of the compressive strength compared to the control specimen is not obvious. This is because the AF content is so little that it only has a weak delaying and constraining effect on LFC cracks, and the macro expression is that the development of compressive strength is not substantial. The highest compressive strength achieved is 1.71 N/mm² on day-56 with the inclusion of 0.45% AF; meanwhile, the lowest compressive strength is 0.87 N/mm² on day-7 which is the control mix. Moreover, the compressive strength value on day 7 showed slight increases from 0.87 N/mm² with the control mix to 1.34 N/mm² with 0.45% AF. After that, it decreased to 1.12 N/mm² 0.6% in addition to AF in LFC. On day-28, the compressive strength increases from 1.05 N/mm² with control mix until 1.5 N/mm² with 0.45% AF and decreases until 1.26 N/mm² with 0.6% AF. This result also shows the increasing trend of compressive strength on day-56, which starts from 1.18 N/mm² on the control mix until 1.71 N/mm² with 0.45% of AF and starts to decrease at 1.26 N/mm² with 0.6% of AF. LFC has lower compressive strength according to the control mix's result in the graph. A higher amount of foam creates a higher amount of air voids and lowers the density. Moreover, the age of concrete also influenced the compressive strength value of LFC. The longer the testing age, the higher the compressive strength of the LFC, as can be seen in the comparison between day-7 and day-56 according to the graph. This weakness can be improved with the addition of AF as shown in the result. AF can control the crack on LFC, and it can strengthen the bonding between the matrixes [35]. Hence, it can be concluded that AF contributes to the enhancement of the compressive strength of LFC at a maximum weight fraction of 0.45%. At this optimum weight fraction of 0.45%, the random dispersal of AF in the LFC matrix forms a network structure, which creates a common stress framework with the LFC matrix. When the LFC is subjected to axial compressive load and generates microscopic cracks, the stress is transmitted from the LFC cementitious matrix to the AF between the cracks due to the bond force between the AF and the LFC. And the AF consumes energy in the process of deformation and pulling out so that the microscopic cracks of the LFC were delayed and inhibited [36]. Beyond the optimum level of AF, agglomeration and the non-uniformity dispersion of BFF were seen, which results in a drop in compressive strength (at 0.45% weight fraction of AF). Additionally, when the AF content in LFC is too high, the distance between each AF is lessened or even the AF contacts [37]. Furthermore, the bond between the AF and the LFC matrix cannot completely work, and the bond effect is decreased. If the AF content is too high or the AF is not evenly dispersed in the LFC matrix, the compressive strength of concrete will be adversely impacted. Moreover, the high amount of AF in FC will retard the process of hydration hence leading to low compressive strength [38]. Considering that the LFC matrix has numerous voids of varying size and shape and the presence of micro-cracks at the transition area between matrices, using AF fibre facilitates regulating failure characteristics when subjected to compressive loads [39].

Figure 6

Flexural strength is the ability of the material to withstand bending forces applied perpendicular to its longitudinal axis. Fig. 7 exhibits the flexural strength of 550kg/m³ of LFC in addition to various percentages of AF. The result presented in Fig. 7 shows that the highest value of flexural strength is 0.61 N/mm² on day-56 with the inclusion of 0.45% AF; meanwhile, the lowest value of flexural strength is 0.2 N/mm² on day-7 with the control mix specimen. The result of flexural strength climbed from 0.20 N/mm² with control mix to 0.37 N/mm² with 0.45% AF on day-7 and started to decrease at 0.6% AF, 0.23 N/mm². In addition, on day-28 and day-56, the result shows an increment from 0.23 N/mm² to 0.46 N/mm² and 0.27 N/mm² to 0.51 N/mm², respectively with addition of 0.15%, 0.35% and 45% AF. However, the LFC with 0.60% AF decreased to 0.28 N/mm² and 0.36 N/mm² on day-28 and day 56. This can be explained by AF which might be failed to fill the matrix. This decreased trend has occurred at a certain amount of AF on day-7, day-28, and day-56. LFC has a lower ratio of flexural to compressive strength, ranging between 0.2 to 0.4 compared to standard concrete. However, with the addition of AF, the flexural strength has been improved because it can change the character of the material from being brittle to ductile. It should be pointed out that the plastic zone of the LFC during flexural resistance improves remarkably after adding AF, and the plastic zone of the LFC improves with the increase of the AF content up to the optimum weight fraction [40]. The reason is that the flexural stress at the crack can be transmitted from the LFC matrix to the AF and then to the LFC matrix at the other end of the AF after the AF is integrated into the LFC. In the process of transferring stress, the AF will deform and pull out to some extent, which consumes part of the energy, thus impeding and preventing the crack of LFC. Stress is slowly transmitted from the middle of the prism to both ends of the prism, which permits the plastic zone of the prism to expand to both ends [41]. However, disproportionate AF inclusion of more than causing weight fractions to exceed 0.45% led to lower cohesion between AF and the cementitious matrix [42]. Besides, it will also decrease the spacing between the AF and even cause the AF to contact each other and reunite. When the bond between the AF and the LFC matrix is reduced, so the flexural strength is diminished [43]. An AF weight fraction of 0.45% is ideal for LFC because flexural and compressive strengths are more desirable.

Figure 7

Fig. 8 shows the splitting tensile strength of LFC with a density of 550 kg/m³. The test was held on three different days, on 7, 28 and 56 days. Overall, it is observed that LFC having any weight fractions of AF displays improved splitting tensile strength compared to unreinforced LFC (control specimen). This may occur due to the superior tensile strength of the AF (refer to Table 3). The AF are distributed randomly into the LFC mixture. The AF is oriented in the progressing crack's perpendicular direction, which can take tensile stress and help increase the crack arresting capability or bridging effect in LFC. Besides, the existence of AF can make the LFC more ductile, and the tensile capacity is commonly greater for a ductile material than that of brittle material [44]. Based on the graph, day-56 has the highest splitting tensile strength value, 0.36 N/mm² with 0.45% AF, while day-7 has the lowest reading of splitting tensile strength, 0.12 N/mm² with the control specimen. The LFC with the inclusion of AF has an increasing reading of splitting tensile strength from 0.14 N/mm² to 0.25 N/mm² on day 7. The trend is same with day-28 and day-56 with 0.18 N/mm² to 0.31 N/mm² and 0.24 N/mm² to 0.36 N/mm², respectively. However, it starts to decrease on each test day when the AF exceeds 0.45% in LFC with readings of 0.14 N/mm², 0.22 N/mm² and 0.26 N/mm². This situation happened also with compressive strength and flexural strength. However, the addition of AF in LFC successfully acted as the anchor that holds the matrix together, which helped to improve the splitting tensile strength. No macro crack is envisaged on the surface of the LFC. As no spalling has transpired in the LFC, it can take the extra tensile load before fracture by providing a ductile behaviour. Othuman Mydin et al. [45] reported that the natural fibre length between 19–25 mm could cross both sides of LFC cracks and create a strong bridging between the cracking interfaces. Overall, LFC containing fibres indicates greater ductility than LFC without fibre. Fibre delays the first crack formation across the crack and retards visible cracking. Beyond the optimum level of AF addition, accumulation and the non-regularity spreading of AF were detected, which results in the decline of the tensile strength (starting from 0.60% weight fraction of AF). Splitting tensile strength improved because of higher LFC robustness facilitated by AF. Adding 0.45% fibre enhances LFC tensile strength by enhancing ideal pozzolanic interactions with cement, producing high-density LFC. This implies that the inclusion of AF improves the splitting tensile strength of LFC (all weight fractions tested in this study). The elongation at break of single AF was considered minimal, resulting in exceptional splitting tensile strength when added into LFC. It should be pointed out that the enhancement in splitting tensile strength of LFC is due to the reduction in the formation and development of micro-cracks for distributing comparatively stiffer AF randomly into the LFC mixture. These randomly oriented AF can control the crack propagation and reduce the width of cracks. The cracks will initiate and start to propagate with increasing the tensile stress [46]. When the cracks reach the LFC matrix-AF interfaces, the AF takes additional stress, and the further propagation of cracks is resisted. Besides, the higher hardness and the higher cohesive force of AF produce a strong network skeleton inside the LFC

Figure 8

Fig. 9 illustrates the correlation between the compressive strength and flexural strength of LFC with a density of 550 kg/m³. From the figures, the result of compressive strength and flexural strength scatters and the linear line to illustrate the connection between them. The value of R² shows the relationship between both results of the LFC, when the R2 is close to the value of 1 that means is the best indication that explained the correlation between compressive strength and flexural strength. The density of LFC influences each strength. It can be noted that LFC such as 550 kg/m³ reduces the strength of compression and flexural due to the significant number of voids. It can be observed from the graph, the age of the LFC also influenced its strength of the LFC. In addition, the inclusion of AF also helped to strengthen the compressive strength and flexural strength; as it can be seen, the LFC started to increase with 0.15% AF compared to the control specimen. This is because AF can bond with the matrix, reducing the void in the LFC.

Figure 9

Fig. 10 reveals the association between compressive and tensile strengths for 550 kg/m³, including a variable percentage of AF. The graph demonstrates the R2 value for the linear line through the data, which indicates the correlation between compressive and tensile strengths. The R² of this correlation for each testing day of 7, 28, and 56 days is 0.90, 0.93, and 0.95. respectively. The value of R², which is close to the one, is illustrated by how closely the compressive strength and tensile strength are.

Figure 10