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Abstract
The construction industry is increasingly seeking sustainable alternatives to ordinary Portland cement (OPC) due to its high cost and the significant environmental impact of its production, particularly CO2 emissions. This study explores the use of brewery dry grain ash (BDGA), an abundant agricultural waste byproduct rich in silica and with promising pozzolanic activity, as a partial substitute for OPC in mortar production. BDGA is generated in large quantities by breweries, making it a viable material for sustainable construction practices. Mortar mixes were prepared with BDGA replacement levels of 0%, 5%, 10%, 15%, and 20% and evaluated for their physical, chemical, thermal, and microstructural properties. Although several studies have assessed the influence of BDGA on concrete strength, this research uniquely examines its effect on cement paste soundness, the morphology of BDGA particles, and how their irregular and angular shapes impact workability, consistency, and setting time, areas previously underexplored. The results showed that increasing BDGA content reduced workability and setting time while increasing water demand. However, 5% and 10% BDGA replacements improved compressive strength (5.6% and 14.5%, respectively), bulk density, ultrasonic pulse velocity, and thermal stability, while also reducing water absorption. These findings demonstrate that BDGA, particularly at a 10% replacement level, is a promising, eco-friendly alternative for cement in mortar applications, offering both performance benefits and environmental advantages.
1. Introduction
Cement serves as the primary binding material in the construction industry worldwide [1–3]. Typically, about 1.65 tons of limestone (1.5–1.8 tones) and 0.4 tons of clay are quarried for each ton of cement production [4]. However, the process of burning Portland-cement clinker at the necessary temperatures is costly due to high fossil fuel consumption [3].
Therefore, there is a global need for environmentally friendly construction materials to reduce CO2 emissions, conserve nonrenewable energy resources, create aesthetically pleasing and healthy environments, and minimize waste [5–7]. Energy, resource, and cost efficiency can be achieved by reducing the amount of cement used and incorporating supplementary cementitious materials (SCMs), which require less heating during processing and emit lower levels of CO2 [8]. According to the authors in [2], 1.5 tons of raw materials are required to produce one ton of ordinary Portland cement (OPC).
Studies conveyed that ground granulated blast furnaces safely ash, Rice husk ash, and silica fume are experimented with alternative ways to replace cement [9, 10]. Some researchers also conduct research on agrowaste pozzolans and brewery dry grain ash’s (BDGA) performance with respect to similar SCMs [11–13]. While some researchers are exploring the use of readily accessible and inexpensive BDGA as a cement substitute, further scientific and technical research is needed to assess the sensibleness of replacing OPC with BDGA through advanced experimental inquiries. According to the authors in [14], incorporating BDGA into a mortal results in an increase in setting time, while compressive strength decreased as the replacement level rose.
As per the authors in [15], spent brewers’ grain is the most abundant byproduct of brewing, accounting for 85% of the total byproducts generated, 31% of the original malt weight, and 20 kg per 100 L of beer produced. There are 12 beer factories producing wet brewery spent grain (WBSG) and brewery spent yeast (BSY) [16]. It was reported by the authors in [17] that the breweries in Ethiopia can produce between 160,000 and 320,000 tons of WBSG residual and 20,000–28,000 tons of BSY. In general, the exact abundance of BDGA can vary widely, as it is produced in significant quantities by breweries as a byproduct of the brewing process. Based on this, BDGA was chosen due to its high silica content and potential pozzolanic activity, as well as its abundance as an agricultural waste byproduct, which aligns with sustainability goals in construction materials. Various studies have analyzed the effect of BDGA on concrete properties, but its impact on the soundness of cement paste, the shape of BDGA particles, and how its shape influences workability, consistency, and setting time have not been thoroughly examined.
This thesis investigates the effect of BDGA as partial cement replacement in mortar on the fresh properties, mechanical properties, durability and microstructure, compressive strength, sulfate attack resistance, ultrapulse velocity (UPV), porosity, water absorption, thermogravimetric analysis (TGA), differential thermal analysis (DTA), and SEM analysis. The study discovered that BDGA can potentially substitute cement and it can be used as cementous material. In addition, the partial replacement of cement with BDGA has advantages by reducing the problem of waste accumulation and simultaneously helping the preservation of natural resources needed for cement production.
2. Materials and Methodology
2.1. Materials
The main ingredients used in this study include brewery dry grain from the Gondar Beer Factory in Ethiopia, OPC, sand, and water. The proportion of these key materials varies based on factors such as workability and strength.
2.1.1. Water
Potable water, sourced from the Bahir Dar University Institute of Technology material testing lab, was used for the concrete mix, and no tests were conducted on the water.
2.1.2. Cement
Dangote OPC grade of 42.5 N was used.
2.1.3. Fine Aggregate
Lalibela river sand, which meets ASTM C33 standards, was used as shown in Table 1. This natural (river) sand has low silt content and a black color, making it of good quality for the investigation. It was sieved using standard ASTM sieves.
| No | Test description | Result | Standard |
|---|---|---|---|
| 1 | Silt content (%) | 2.33 | ASTM C117 |
| 2 | Moisture content (%) | 1.45 | AASHTO T 255-00 |
| 3 | Unit weight (g/cm3) | 1.32 | AASHTOT19/T 19M00 |
| 4 | Apparent specific gravity | 2.48 | AASHTO T84 C128 |
| 5 | Bulk specific gravity (BSG) | 2.75 | AASHTO T84 C129 |
| 6 | BSG (SSD basis) | 2.75 | AASHTO T84 C130 |
| 7 | Absorption capacity (%) | 2.56 | AASHTO T84 C131 |
| 8 | Fineness modulus | 2.86 | ASTM C33 |
2.1.4. BDGA
Brewery dry grain (Figure 1(a)) was sourced from the Dashen Beer Factory in Gondar, northern Ethiopia. After initial crushing, it was milled and burned at 650°C for six hours, tand hen sieved (75 μm) to produce BDGA (Figure 1(b)). Its chemical composition was analyzed by the Geological Survey of Ethiopia, and its physical properties are listed in Table 2.
Figure 1 (a)
Figure 1 (b)
| No | Measurements | Results |
|---|---|---|
| 1 | Loose bulk density | 1584.5 |
| 2 | Dry-roded weight | 1905.5 |
| 3 | Bulk specific gravity (SSD) | 2.79 |
| 4 | Water absorption (%) | 1.52% |
3. Methods
The research was conducted at Bahir Dar University, Bahir Dar Institute of Technology (BIT), Ethiopia, in the construction material and structural laboratory. The study examines the impact of substituting cement with BDGA on mortar strength. Various tests were executed, including fresh properties (setting time and workability), mechanical properties (compressive strength and UPV), durability (water absorption, porosity, and sulfate resistance), and microstructure analysis (SEM, TGA, and DTA) over curing periods of 3, 7, 28, and 56 days. For each test, BDGA was used as a replacement for 5%, 10%, 15%, and 20% of the cement by weight, the replacement levels were chosen to evaluate the performance trend and identify the optimal substitution point for practical applications, A fixed water-to-cement ratio of 0.485 was selected after preliminary trials, as it provided workable consistency and was consistent with other pozzolanic mortar studies. This ratio was maintained across all mixes to ensure valid performance comparisons. Three cubes of 50 mm × 50 mm × 50 mm size were used for each replacement level, including the control mix. The mix design determined the number of molds and the quantity of materials based on ASTM C109 standards. In total, 195 cubes (39 cubes per mix) were prepared for the study. Initially, a trial mix of 30 cubes was tested for 7- and 14-day mortar compressive strength to predict the effect of cement replacement with BDGA. A mortar mix ratio of 1:2.75 (cement: sand by weight) was adopted based on ASTM C109 standards. After 24 h of casting, the samples were removed from the molds and transferred to a curing tank according to ASTM C192 standards until the tests were conducted.
4. Results and Discussion
4.1. Physical Properties of BDGA
According to the authors in [18], surface area is the means through which a solid interacts with its surroundings, especially liquids and gases. The surface area is the most meaningful morphological characteristic of solid substances in applications related to porous structures, such as industrial adsorbents [19]. The BET result (Table 3) shows the surface area of OPC and BDGA, which are 339 m2/g and 494 m2/g, respectively. It can be seen that BDGA have a 155 m2/g larger surface area compared to the OPC cement. This high surface area value of BDGA has an effect on mortar to have high early strength and low bleeding but high water is needed for constant consistency.
| No. | OPC∗ | BDGA | ||
|---|---|---|---|---|
| 1 | Surface area data |
|
|
|
| 2 | Pore volume data |
|
|
|
| 3 | Pore size | HK method pore radius (Å) | 8.13E + 00 | 8.612E + 00 |
| Data SF method pore radius (Å) | 1.62E + 01 | 1.652E + 00 | ||
| NLDFT pore radius (Å) | 1.32E + 01 | 1.324E + 01 | ||
| 4 | Relative density/specific gravity (g/cm3) | 3.15 | 2.75 |
The Horvath–Kawazoe (HK) method provides the modal diameter of pores in the BDGA under analysis [20]. The pore size distribution results indicated modal values near 1.324e + 01 Å (1.32 nm), suggesting a predominance of nanopores. As shown in Table 3, OPC has a larger pore radius and volume compared to BDGA. The larger pore size and radius in OPC are a result of the dehydration process during temperature treatment, which leads to the formation of microspores and cracks. In contrast, the smaller pore size and volume in BDGA are due to its higher fineness and surface area.
4.2. Chemical Composition of BDGA
The chemical analysis was performed using the complete silicate analysis method at the Ethiopian Geological Survey Institute. The oxide composition of the finer BDGA grains is shown in Table 4, indicating a high silica content of 48.9%. Silica is known to contribute to strength development in concrete [21], suggesting that the reactivity of BDGA makes it suitable for partial replacement of cement in structural concrete or mortar production.
| Chemical | SiO2 | Al2O3 | Fe2O3 | CaO | MgO | Na2O | K2O | SO3 | LOI |
|---|---|---|---|---|---|---|---|---|---|
| BDGA | 74.20 | 1.32 | 0.82 | 3.33 | 3.44 | 0.24 | 7.29 | 0.5 | 4.21 |
Referring to ASTM C618, BDGA can be categorized as Class N natural pozzolan material as SiO2 + Al2O3 + Fe2O3 = 76.34 > 70%, which much more agrees with the mineralogical analysis conducted by the authors in [14, 22]. ASTM C150 and Bogue’s equations were applied to calculate the potential cement phase composition for the main binder percentages. BDGA contains 4.87% tricalcium aluminate (C3A), which releases a small amount of heat during the initial hydration and hardening phases and contributes slightly to the later strength development. Cements with low C3A content are more resistant to sulfates present in soils and waters. Furthermore, the tetracalcium aluminoferrite (C4AF) content in BDGA is 2.49%, which results from the use of iron and aluminum raw materials.
4.3. SEM of BDGA
The microscopic image of the BDGA particle is shown in Figure 2 with ×1500 and ×600 resolution.
Figure 2
Microscopic analysis showed that BDGA particles are angular, irregular, and rough, with many exhibiting a porous structure. This microstructure increases water demand and reduces the workability of cement mortar when BDGA is used as a supplementary material.
4.4. Effect of BDGA on Cement Paste
4.4.1. Consistency
Consistency reflects the density or stiffness of cement and the water content of the standard paste, typically ranging between 26% and 33%. Setting refers to the gradual loss of workability in concrete over time.
As per the result depicted in Figure 3, the partial replacement of BDGA increases the water demand for the normal consistency of cement. This was due to the fineness of the BDGA particles. The same pattern was also observed in a study by [14], stating that the quantity of water required for attaining normal consistency increased as the percentage replacement of cement by BDGA increased.
Figure 3
4.4.2. Setting Time
Figure 4 shows that the initial setting time of the control mix was longer than that of all BDGA replacement percentages. The initial setting times ranged from 45 to 75 min, while the final setting times ranged from 120 to 255 min, meeting the requirements of ASTM C191. Both the initial and final setting times decreased as the percentage of BDGA replacement increased. The dissolved BDGA form a dense network that acts as a barrier, preventing the needle from easily penetrating the paste, thus leading to a faster setting time.
Figure 4
4.4.3. Soundness
The soundness of cement is primarily affected by the presence of excess lime (CaO) in the cement.
Figure 5 shows that at 5% replacement, the specimen’s soundness remained stable. At 10% replacement, expansion was similar, and beyond 10%, expansion increased as the replacement level rose. This is because the small amount of free magnesium oxide (f-MgO) at 5% acts as a filler, while higher replacement levels result in more f-MgO, leading to greater expansion. The reasons for poor dimensional stability are as follows: the free calcium oxide (f-CaO) and/or the f-MgO in the clinker is too much, or the gypsum mixed in the clinker is excessive [23].
Figure 5
4.5. Workability of Mortar Mixes (Slump Test)
According to ASTM C270, laboratory mortar must achieve a slump of 110 ± 5%. Field mortar should be mixed with the maximum water quantity to maintain workability while meeting the initial absorption rate of masonry units. Laboratory mortar qualities are maintained at a rate of 110 ± 5% (ASTM C270, 2013).
Figure 6 illustrates that BDGA replacement affects the mortar’s workability at a constant water-to-cement ratio. As the BDGA percentage increases, the mortar slump decreases. The control mix exhibited superior and better workability, despite requiring less water for standard cement paste consistency. The porous surface of BDGA absorbed some of the mixing water. Furthermore, the high surface area and highly irregular shape of the BDGA from the morphology made the workability of the BDGA stiffer than the control mix [24].
Figure 6
4.6. Physical and Mechanical Properties of Mortar
4.6.1. Bulk Density
The bulk density of mortar, based on saturated surface dry (SSD) weight, was measured for different mix compositions at various curing ages. As shown in Figure 7, the highest bulk density of 3060 kg/m3 was recorded on Day 56 with 10% BDGA, while the lowest density of 2990 kg/m3 occurred on Day 3 with 20% BDGA. The bulk density increased from 3025 kg/m3 to 3040 kg/m3 on Day 28 and from 3040 kg/m3 to 3060 kg/m3 on Day 56 as the BDGA content increased from 0% to 10%.
Figure 7
Compared to the control mix, the BDGA mix with 10% replacement (BDGA-10%) shows a higher bulk density. On the 56th day, BDGA-10% performs better (3060 kg/m3) than the control mix (3040 kg/m3), which aligns with the findings of State et al. (2000). The larger surface area of BDGA contributes to this higher bulk density at later ages by filling the pores. The 10% BDGA replacement exhibited a competitive bulk density with the control mix, and the density of the specimens increased with curing age. However, as the BDGA replacement percentage exceeds 10%, the bulk density decreases sharply, particularly at early ages. This may be due to the increased porosity and less efficient packing of the mix at higher replacement levels.
4.6.2. Compressive Strength
Compared to the control mix, 10% BDGA replacement exhibited the highest compressive strength across all curing days, with the peak value recorded at 56 days. Even 5% BDGA replacement demonstrated greater compressive strength than the control mix (Figure 8). At 28 days, 10% BDGA showed a 14.5% increase in compressive strength, while 5% BDGA resulted in a 5.6% increase. At 56 days, 5% BDGA showed a 3.5% improvement in compressive strength over the control mix.
Figure 8
The pozzolanic nature of BDGA results in an increase in compressive strength up to BDGA-10 due to pozzolanic reaction, i.e., the transportation of calcium hydroxide (CH) via water to combine with the aluminate and/or silicate clay minerals amount of SiO2. With increased curing time, the hydration reaction may contribute to the hydration product and improve compressive strength in the BDGA specimens [14]. In addition, the high surface area of BDGA enhances its fineness, which directly impacts hydration, setting, hardening, strength, and heat of hydration. For mixes with BDGA content exceeding 10%, the mix requires higher water demand, leading to unreacted siliceous material.
4.6.3. Ultrasonic Pulse Velocity Test
As illustrated in Figure 9, the ultrasonic pulse velocity of cement mortar increased as the percentage of BDGA increased up to 10%. The UPV values of all BDGA mortar increased with the curing age of the mortar.
Figure 9
As per BS 1881-203:2004 and as shown in Table 5, the quality of the concrete, in terms of uniformity and mortar strength, was moderate at early stages up to a 10% BDGA replacement, with improved strength observed at later ages. This can be attributed to the high calcium content in OPC and the silicate materials in BDGA, which enhance hydration and promote the formation of calcium–silicate–hydrate (C–S–H) gel. The formation of these gels helps refine the pores in the hardened mortar, resulting in a more compact structure that enhances UPV, compressive strength, and durability.
| No | Pulse velocity (km/sec) | Concrete quality grading |
|---|---|---|
| 1 | Above 4.5 | Excellent |
| 2 | 3.5 to 4.5 | Good |
| 3 | 3.0 to 3.5 | Medium |
| 4 | Below 3.0 | Doubtful |
4.7. Durability Properties of Mortar
4.7.1. Sulfate Attack Resistance
Sulfate attack significantly affects mortar durability. As shown in Figure 10, compressive strength loss decreases with up to 15% BDGA replacement, reflecting similar trends in pure water. As a Class N pozzolan, BDGA improves density and resistance to chemical attacks. Strength loss from sulfate exposure increases with curing time, peaking at 56 days.
Figure 10
As shown in Figure 10, the average reduction in compressive strength due to sulfate attack across all mixes ranges from 0.8 MPa to 2.10 MPa. Specifically, for the 28th day, the reduction ranged from 0.8 MPa to 2.0 MPa, while at 56 days, it ranged from 0.95 MPa to 2.10 MPa. These results indicate that sulfate attack has a minimal effect on the mortar, especially at early ages. The BDGA-5% and BDGA-10% mixes demonstrated good performance against sulfate attack.
4.7.2. Water Absorption
Water absorption of mortar decreased with increasing BDGA content up to 10% cement replacement, as shown in Figure 11. The water absorption of the mixtures ranged from 5% to 11.5%, with a significant reduction in water absorption observed over time.
Figure 11
The increased formation of hydration products during curing reduced the internal porosity of the concrete, leading to lower water absorption. As curing progressed, the improved hydration of raw materials enhanced the density of the mortar, further reducing water absorption. However, in mortar specimens with BDGA content exceeding 10%, water absorption increased. This is due to the higher porosity of BDGA and its increased water affinity, owing to its large surface area. Linear regression analysis showed a strong relationship between compressive strength and water absorption, with higher compressive strength corresponding to lower water absorption, as shown in Figure 11.
4.8. Microstructure Tests of Harden Mortar
4.8.1. Scanning Electron Microscopy
As can be seen in Figure 12, C–S–H, portlandite (CH), and pore are observed in the sample. The main hydration products, CH and C–S–H, were identified based on their morphology. The C–S–H formed has a dense fibrillar structure, similar to the morphology (Bagasse et al., 2014). Less dense microstructure is observed with a lot of pores, furthermore, compared to the BDGA-5 and BDGA-10 mixes a significant amount of portlandites (CH) are observed.
Figure 12
4.8.2. TGA
TGA was used in the study and development of a variety of chemicals to determine their thermal stability and composition of the mortar sample after replacing BDGA with three replacement proportions (0%, 10%, and 15%) for 28 days of curing and to examine the contents of bound water (H), CH, and calcium carbonate. TGA is a technique in which the mass of a polymer is measured as a function of temperature or time while the test is carried out in a controlled environment. TGAs have temperature ranges of around 1000°C or higher, which is a sufficient top limit for polymer applications. TGA was performed on the cement pastes at 7, 28, and 56 days.
From the TGA curve shown in Figure 13, it is observed that significant weight loss can occur in many ways. The primary effect from 25°C to 100°C had to do with the residual pore water which evaporated from capillary pores [25]. In this stage, the weight loss depended upon the adsorbed water, interlayer water, and capillary pores.
