Concrete Innovation Using Tree Branch Waste as Coarse Aggregate and Stone Ash as Fine Aggregate ^†

Abstract

Concrete is a widely used construction material. This research investigates the effect of adding tree branch waste and stone dust as substitutes for coarse and fine aggregates on concrete’s physical and mechanical properties. The results show that these additives significantly impact weight and compressive strength. The weight comparison for 10% additive concrete was 7.28 kg at 7 and 14 days, while for 20% additive concrete, it was 7.02 kg at 7 days and 7.06 kg at 14 days. Normal concrete weighed 7.50 kg at 7 days and 7.66 kg at 14 days. The planned compressive strength (K250 or F’c: 20 MPa) for 28 days was met, with samples containing 10% and 20% additives exceeding the planned strength. However, increased use of these materials led to a reduction in compressive strength. Therefore, the addition of tree branches and stone dust should be limited to 10%, as the highest compressive strength was obtained at this percentage. This research suggests that using tree branch waste and stone dust as partial substitutes for aggregates can reduce concrete’s weight while maintaining its strength. Limiting the addition to 10% is recommended for optimal results.

1. Introduction

Concrete is a commonly used construction material in civil engineering. Almost every civil engineering structure, including buildings, bridges, and water infrastructure, incorporates concrete. The self-weight of concrete plays a crucial role in structural design; as the structure’s weight increases, the seismic forces acting upon it also increase. Consequently, larger foundation dimensions or higher compressive strength are required to withstand structural loads, leading to increased construction costs. The use of additional materials such as tree branches and stone dust in concrete can help reduce its overall weight, offering a viable alternative solution to this problem. The principle behind this innovation is the introduction of air voids within the concrete, achieved through the use of substitute aggregates and filler materials [1].

However, the presence of air voids can impact the compressive strength of concrete. Therefore, in this experimental study, stone dust is incorporated as a partial fine aggregate replacement to compensate for the potential reduction in compressive strength caused by the inclusion of tree branches. Innovation in civil engineering is essential, particularly in addressing existing challenges, including the incorporation of alternative materials as substitutes for coarse and fine aggregates [2]. Such aggregates can come from tree waste, which is often considered useless and left to decay. Some people, however, still find value in tree branches, using them as firewood, especially in rural areas [3]. Burning wood, however, releases smoke and contributes to air pollution, posing health hazards when inhaled continuously. Similarly, improper disposal of stone dust can also have adverse effects on human health. Given these issues, innovative approaches are required to repurpose tree branch waste and stone dust into productive materials, reducing reliance on natural resources while mitigating environmental and health impacts [4].

2. Materials and Methods

2.1. General Overview

This research was conducted experimentally at the laboratory of Nusa Putra University, Sukabumi. The study began with an extensive literature review to establish a foundation for addressing the identified problem. The primary materials used in this study include tree branches and stone dust. Additional materials used in the concrete mixture are cement, fine aggregate (sand), and water. The research was conducted in mid-January 2025.

2.2. Research Stages

This research will be conducted in several stages, namely the preparation stage, the implementation stage, and the analysis and discussion stage. A general overview of these research stages can be seen in the flowchart diagram, please see on the Figure 1 [5].

2.3. Material Preparation Stage

The materials used in this study are as follows:

• Tree branches: The tree branches used in this study were collected from a garden near the author’s residence.
• Stone dust: Obtained from a batching plant located in Sukabumi Regency.
• Coarse aggregate: Jebrod gravel, commonly used in normal concrete production, was selected based on compatibility with the size of tree branches.
• Fine aggregate: Jebrod sand was used as the fine aggregate in this study.
• Cement: Portland Cement Type 1 from PT. Semen Tiga Roda, packaged in 50 kg paper bags.
• Additives: A combination additive, Sika Viscocrete 3115 N (Superplasticizer Water Tight), was used at a dosage of 2.5 mL/0.003375 m³.
• Water: Sourced from well water.

2.4. Concrete Sample Preparation

This study focuses on testing cube-shaped concrete specimens with dimensions of 15 cm × 15 cm × 15 cm. The testing will be conducted at 7 days and 14 days of curing, with sample distribution as follows:

Based on

Table 1. Laboratory Testing Sample Data.

% Additional Material	Concrete Substitute				Normal Concrete		Total
	10% Tree Branch and Stone Ash		20% Tree Branch and Stone Ash
	Concrete Age
	7	14	7	14	7	14
Normal					1	1	2
10%	1	1					2
20%			1	1			2
Total Overall Sample							6

below, a total of six samples will be tested. These include two normal concrete samples, one tested at 7 days and the other at 14 days. Additionally, there will be two innovative concrete samples with a 10% substitution of tree branches and stone dust, tested at 7 days and 14 days, respectively. Finally, two innovative concrete samples with a 20% substitution of tree branches and stone dust will also be tested at 7 days and 14 days, respectively.

2.5. Concrete Compressive Strength Testing

The concrete strength test was conducted using a Compression Testing Machine [6]. at the Nusa Putra University laboratory in Sukabumi. This test was performed to determine the compressive strength of the prepared specimens. The testing was carried out when the concrete specimens reached 7 and 14 days of curing. Due to time and budget constraints, only one sample was used for each variation of the additional materials.

2.6. Data Analysis

The data obtained from laboratory testing was analyzed to determine the compressive strength and weight of the concrete. This analysis allows for a comparison between normal and lightweight concrete [7]. The final output is presented in the form of diagrams and graphs.

3. Results

3.1. Research Findings

The final stage of this research includes material testing results and compressive strength tests conducted at the Nusa Putra University laboratory.

3.1.1. Material Testing Results

Before preparing the precast concrete test specimens, the materials used were tested to determine their quality for incorporation into the concrete mixture [8]. This material testing aimed to assess the suitability of the materials in maintaining the desired concrete properties [9].

This table presents the physical properties of the aggregates used in the study, highlighting key parameters such as organic content, silt content, bulk density, and moisture content. Based on

Table 2. Data on physical properties of aggregates.

a	Type of Test		Aggregate
			Fine Aggregate (Jebrod Sand)	Coarse Aggregate (Jebrod Gravel)	Stone Ash	Tree Branche
1	Organic Content (%)		2.20%	-	-	-
2	Silt Content (%)		3.25%	-	-	-
3	Bulk Density (kg/L)	solid	0.840 Kg/L	1.612 Kg/L	0.120 Kg/L	0.188 Kg/L
		loose	0.800 Kg/L	1.215 Kg/L	0.095 Kg/L	0.237 Kg/L
4	Moisture Content (%)		3.4%	4%	3%	11%

on the results of testing the physical properties of aggregates, the water content figures are obtained for each test specimen of jebrod sand: 3.4%, gravel: 4%, stone ash: 3%, tree branches: 11%.

3.1.2. Mix Design of Concrete Mixtures

To determine the strength quality of normal concrete using coarse aggregate (gravel) and fine aggregate (sand), the K250 concrete strength class (f’c) 20 MPa was used. Aggregate composition consisted of 35% sand and 65% crushed stone, with a water–cement ratio (W/C) of 0.75 [9].

3.1.3. Compressive Strength Test Results in the Laboratory

The compressive strength test results for normal concrete and innovative concrete with tree branch waste as a partial coarse aggregate replacement and stone ash as a partial fine aggregate replacement (0%, 10%, and 20%) at the ages of 7, 14, and 28 days were calculated using standard formulas in accordance with Indonesian National Standards (SNI), please see on the

Table 3. Compressive Strength Test Results for Normal Concrete and Innovative Concrete Using Tree Branch Waste and Stone Ash at 7 Days.

Age	Weight	Load		Area	Volume	Weight Volume	Compressive Strength	Compressive Strength
(Days)	(Kg)	(KN)	(Kg)	(cm2)	(m3)	(Kg/m3)	(Kg/cm2)	(MPa)
0% Tree branches and stone/concrete ash NORMAL
7	7.50	395	40,278.15	225	0.003375	2222.222	179.546	17.56
10% Tree branches and stone ash Innovation Concrete
7	7.28	350	35,689.50	225	0.003375	2157.037	158.620	15.56
20% Tree branches and stone ash Innovation Concrete
7	7.02	315	32,120.55	225	0.003375	2080.000	142.758	14.00

and

Table 4. Estimated Compressive Strength Analysis of Concrete at 28 Days with an Estimate Factor for 7 Days = 0.65.

Concrete Age Estimate Number	Estimated Compressive Strength of 28 Days Old Concrete	Estimated Compressive Strength of 28 Days Old Concrete
	(Kg/cm2)	MPA
0% Tree branches and stone/concrete ash NORMAL
0.65	275.406	27.017
10% Tree branches and stone ash Innovation Concrete
0.65	244.031	23.939
20% Tree branches and stone ash Innovation Concrete
0.65	219.628	21.545

below.

Based on Table 3, the compressive strength test results for concrete at 14 days indicate a reduction in the weight of the innovative concrete compared to normal concrete. However, the reduction observed in the table is not significantly noticeable.

The estimated compressive strength of concrete at 28 days was analyzed based on an estimation factor of 0.65 for 7-day-old concrete. The results indicate that the incorporation of tree branches and stone/concrete ash as additional materials affects the compressive strength of the concrete. Normal concrete without any additives showed the highest estimated strength, while increasing the proportion of added tree branches and stone ash led to a gradual reduction in compressive strength. The detailed values of estimated compressive strength in both Kg/cm²; and MPa for different mix compositions are presented in Table 4.

Based on Table 4, the estimated compressive strength of concrete at 28 days shows a decrease as the proportion of innovative materials increases. However, the compressive strength remains above the planned target. Furthermore, calculations indicate that using 10% tree branch (RP) and stone ash (AB) substitution can reduce the need for coarse and fine aggregate by 10%.

The results indicate that the addition of supplementary materials leads to a gradual decrease in the compressive strength of concrete. This reduction suggests that the mechanical properties of concrete are highly sensitive to changes in aggregate composition, particularly when natural aggregates are partially replaced by alternative materials. The trend highlights that although supplementary materials may offer environmental and economic benefits, their excessive use compromises the structural performance of concrete. Such a relationship between material proportion and compressive strength is clearly demonstrated in Figure 2.

To evaluate the effect of substituting conventional aggregates with tree branches and stone ash, compressive strength tests were conducted on concrete specimens at the age of 14 days. The specimens were prepared with varying substitution levels of tree branches as coarse aggregate (0%, 10%, and 20%) while stone ash was used as fine aggregate. The test results provide insights into the influence of these substitutions on the density, load-bearing capacity, and compressive strength of the concrete. The detailed results of the compressive strength tests are presented in

Table 5. Compressive Strength Test Results for Normal Concrete and Concrete Substituted with Tree Branches and Stone Ash at 14 Days.

Age	Weight	Load		Area	Volume	Weight Volume	Compressive Strength	Compressive Strength
(Hari)	(Kg)	(KN)	(Kg)	(cm2)	(m3)	(Kg/m3)	(Kg/cm2)	(MPa)
0% Tree branches and stone/concrete ash NORMAL
14	7.66	580	59,142.6	225	0.003375	2269.630	262.856	25.79
10% Tree branches and stone ash Innovation Concrete
14	7.28	490	49,965.3	225	0.003375	2157.037	222.068	21.78
20% Tree branches and stone ash Innovation Concrete
14	7.06	430	43,847.1	225	0.003375	2091.852	194.876	19.12

.

As shown in Table 5, the compressive strength of concrete decreases with increasing substitution of tree branches and stone ash. Normal concrete (0% substitution) achieved the highest compressive strength of 25.79 MPa, while the 10% substitution resulted in a reduction to 21.78 MPa, and further decreased to 19.12 MPa at 20% substitution. This trend indicates that although tree branches and stone ash can be utilized as alternative aggregates, their higher proportions significantly reduce the mechanical performance of concrete. The decline in compressive strength is mainly attributed to the lower density and weaker bonding characteristics of the substituted materials compared to natural aggregates. The estimated compressive strength of concrete at 28 days, calculated from 14-day strength using a conversion factor of 0.88, shows that higher percentages of tree branches and stone ash substitution result in lower compressive strength, as presented in

Table 6. Results of the Analysis of the Estimate of Concrete Compressive Strength at the Age of 28 Days with the Estimated Figure for 14 days = 0.88.

Concrete Age Estimate Number	Estimated Compressive Strength of 28 Days Old Concrete	Estimated Compressive Strength of 28 Days Old Concrete
	(Kg/cm2)	MPA
0% Tree branches and stone/concrete ash NORMAL
0.88	298.700	29.302
10% Tree branches and stone ash Innovation Concrete
0.88	252.350	24.756
20% Tree branches and stone ash Innovation Concrete
0.88	221.450	21.724

.

Based on Table 6, the estimated compressive strength values at 28 days indicate that increasing the proportion of innovative materials results in a decline in compressive strength. However, the compressive strength remains above the planned target, ensuring structural feasibility.

The compressive strength of concrete decreases as the proportion of tree branches and stone ash increases, with normal concrete recording 25.79 MPa, 10% substitution 21.78 MPa, and 20% substitution 19.12 MPa, as shown in Figure 3. Based on the analysis, the optimal substitution level should be limited to 10%, as it provides the closest strength value to normal concrete while still reducing aggregate usage.

Based on Figure 3, increasing the proportion of additional materials reduces the compressive strength of concrete. The calculations show that 10% substitution of tree branches (RP) and stone ash (AB) decreases the need for coarse and fine aggregates by 10%, while 20% substitution achieves 20% savings. This indicates that higher substitution levels reduce aggregate demand. However, since the compressive strength results suggest that the 10% replacement sample performs closest to normal concrete, the use of supplementary materials should be limited to 10%.

4. Discussion

This research shows that the addition of Supplementary Materials such as tree branches and stone ash as partial replacements for coarse and fine aggregates can affect the physical and mechanical properties of concrete. The research findings indicate that the addition of 10% and 20% Supplementary Materials can reduce the weight of concrete while still meeting the planned compressive strength target. Some important findings from this research are

• Weight Reduction: The addition of 10% and 20% Supplementary Materials can reduce the weight of concrete, which can be beneficial in reducing structural loads.
• Compressive Strength: Although the addition of Supplementary Materials can reduce the compressive strength of concrete, it still meets the planned compressive strength target of K250 or F’c: 20 MPa at 28 days.
• Limitation of Supplementary Materials: This research recommends that the addition of Supplementary Materials should be limited to 10%, as this percentage yields the highest compressive strength while maintaining acceptable structural performance.

Thus, this research can contribute to the development of lighter and more environmentally friendly concrete using Supplementary Materials that can reduce environmental impacts. However, further research is needed to further understand the properties of concrete with the addition of these Supplementary Materials.

5. Conclusions

Based on the research findings, the physical and mechanical properties of concrete are significantly influenced by the addition of Supplementary Materials. The compressive strength test results indicate a reduction in the weight of innovative concrete incorporating tree branches and stone ash as partial replacements for coarse and fine aggregates, respectively. A comparison of weight values shows that a 10% additional material results in a 7-day concrete weight of 7.28 kg and a 14-day weight of 7.28 kg, while a 20% additional material leads to a 7-day weight of 7.02 kg and a 14-day weight of 7.06 kg. In contrast, normal concrete weighs 7.50 kg at 7 days and 7.66 kg at 14 days. Regarding compressive strength, the planned design strength was K250 or F’c: 20 MPa at 28 days. The research findings indicate that samples containing 10% and 20% additional materials still met the target compressive strength at 28 days. However, the estimated values reveal a decline in compressive strength as the percentage of Supplementary Materials increases. The graphical representation confirms that increased material substitution leads to lower compressive strength. Therefore, it is recommended to limit the addition of tree branches and stone ash to 10%, as this percentage yields the highest compressive strength while maintaining acceptable structural performance.