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Global Research journal of Natural Science

& Technology (GRJNST)

Volume: 04 - Issue 2 (2026), 2049

ISSN P: 2790-7643 ISSN E: 2790-7651

www.grjnst.net

https://doi.org/10.53762/grjnst.04.02.01

Optimization of GGBS as a Partial Replacement of Cement for Enhanced

Strength and Durability of Sustainable Concrete

Received: 26 December 2025. Accepted: 19 January 2025. Published: 25 March 2026

Tariq Ali

Department of Civil Engineering, The Islamia University

of Bahawalpur, Bahawalpur, Pakistan

ali_tariq06@iub.edu.pk

Abdul Salam Buller

Department of Civil Engineering, NED University of

Engineering & Technology Karachi, Pakistan

engr.salam@cloud.neduet.edu.pk

Samreen Shabbir

Department of Civil Engineering, Dawood University of

Engineering & Technology Karachi, Pakistan

samreen.shabbir@yahoo.com

Muhammad Azam

Department of Civil Engineering, The Islamia University

of Bahawalpur, Bahawalpur, Pakistan

engr.azam35@gmail.com

Mujahid Hussain Lashari

Department of Civil Engineering, The Islamia University

of Bahawalpur, Bahawalpur, Pakistan

dmhlashari@gmail.com

*Corresponding Author: Dr. Zaheer Ahmed

(dr.zaheer@kfueit.edu.pk )

GRJNST, Volume: 04 - Issue 2 (2026) / ISSN P: 2790-7643

Article ID: 2049

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Commons Attribution 4.0 International (CC BY 4.0) license, which permits unrestricted use and distribution

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Abstract: Concrete is one of the most common building materials in the world. It has

great compressive strength, but it is not very durable or sustainable because it relies on

ordinary Portland cement (OPC). Ground Granulated Blast Furnace Slag (GGBS), a by-

product of the steel industry, was used as a partial replacement for Ordinary Portland

Cement (OPC) to improve the mechanical and durability performance of concrete. The

mass proportions for replacing cement with GGBS in concrete mixes were 0%, 10%,

20%, 30%, and 40%. The mix ratio was 1:1.5:3, and the water-to-cement ratio was 0.45.

Mechanical performance was tested by measuring the compressive strength, split tensile

strength, flexural strength, and surface hardness (using the rebound hammer test). For

durability performance carbonation depth and water permeability tests were conducted.

According to the findings, GGBS produced the highest compressive, tensile, and flexural

strengths when 20% of OPC was substituted. It also improved surface hardness and

decreased permeability, indicating increased durability. Mechanical strength, resistance to

carbonation, and permeability all decreased above this point. The results validate the

viability of employing GGBS as a sustainable binder, which lowers CO2 emissions and

cement consumption in environmentally friendly building.

Keywords: Concrete, GGBS, Supplementary Cementitious Materials, Mechanical

Strength, Durability, Sustainable Construction

Introduction

he most popular building material in the world, concrete is renowned for its high workability,

versatility, and compressive strength. Its creation and use serve as the foundation for the development

of infrastructure, particularly in developing nations. However, conventional concrete has a significant

environmental cost, mostly because it uses Ordinary Portland Cement (OPC). About 7–8% of the

world's CO₂ emissions come from the cement industry alone, mostly from the calcination of limestone

and the use of fossil fuels in its manufacture. Because of the urgent need to slow down climate change,

researchers and engineers are looking into low-carbon options like using industrial byproducts as

supplementary cementitious materials (SCMs).

Ground Granulated Blast Furnace Slag (GGBS) is a very popular SCM. When molten slag, which is a

by-product of making iron in a blast furnace, cools quickly, it becomes ground granulated blast-furnace

slag (GGBS), which is a latent hydraulic material. The reaction of its calcium, silica, and alumina-rich

composition with calcium hydroxide gives it strength and durability. This is how ordinary Portland

cement (OPC) turned into more calcium silicate hydrate (C-S-H). The incorporation of GGBS into

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concrete mixtures has been shown to improve several performance characteristics such as permeability,

chloride and sulphate resistance, reduced alkali-silica reaction and pore structure refinement.

Several studies have been undertaken on the use of GGBS in concrete mixtures. Dinakar et al. [32] in

the evaluation of high-volume GGBS concrete increased the durability and porosity refinement also up

to 50% replacement [1]. According to Ahmad et al. Results of previous studies showed that at 20%

GGBS replacement continued pozzolanic reactions promoted compressive and split tensile strength up

to 8 weeks, particularly at 28 and 56 days [2]. In the study of Habert et al., the GGBS environmental

benefits were highlighted. (2020) by mentioning that significant reductions in embodied CO₂ were

achieved without compromising durability. According to Kannan et al. GGBS enhances thermal

cracking resistance and chemical-resistant. [3] However, the slow reactivity of GGBS relative to OPC

may negatively affect the strength performance in the initial periods of life [4]. GGBS-modified

concrete may show delayed strength gain, increased carbonation depth, and variable workability

depending on fineness and curing conditions, according to Umapathy et al. [4] and Sequeira et al [5].

Singh et al. [6] stressed the importance of striking a balance between performance trade-offs and

environmental benefits, particularly when substituting GGBS for more than 30% OPC. Many other

have investigated the mechanical and durability performance of concrete by adding different SCM in

concrete [7–9]

Detailed studies assessing the combined mechanical and durability properties, particularly under

standardized curing conditions, are still scarce, despite the fact that the advantages of GGBS have been

widely publicized. Numerous earlier studies concentrate on mechanical performance or particular

durability metrics, such as chloride ingress or sulfate resistance. Furthermore, the majority of research

uses materials from particular geographical areas, which makes it challenging to generalize the findings.

Regionally based studies that employ locally accessible OPC, aggregates, and GGBS are obviously

needed. These studies should provide a comprehensive performance evaluation that includes slump,

compressive, tensile, and flexural strength in addition to carbonation and permeability resistance.

The present study aims to bridge the research gaps identified through a comprehensive experimental

program that assesses concrete mixtures with partial cement replacement with GGBS. Goals: To assess

the influence of varying percentages of GGBS replacement (10%, 20%, 30%, and 40%) on various test

parameters including mechanical and durability were evaluated. To determine the effects of GGBS on

durability indices such as surface hardness, water permeability and carbonation resistance of concrete.

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The aim is to establish in local material and curing conditions the optimum level of replaceable GGBS

that provides the best combination of durability, mechanical performances, and yes sustainability.

2. Experimental Program

2.1 Materials

The experimental program included materials obtained from local suppliers to ensure that it was

realistic and appropriate. Below is a list of the components that were used:

Cement: The main binder was OPC Type I, which complied with ASTM C150 standards. Its

compressive strength, consistency, and setting time were evaluated.

Fine Aggregates: Good workability and gradation were guaranteed by a 50:50 blend of natural sand

from local market.

Coarse Aggregates: 5–19 mm crushed stones from the local marker were used for making of concrete

samples. The specific gravity of the aggregates ranged from 2.64 to 2.69.

Water: ASTM C1602-compliant clean tap water that can be used to mix and cure concrete.

GGBS: A nearby steel mill provided the ground granulated blast furnace slag. It met ASTM C989

standards with a Blaine fineness of 410 m²/kg and a specific gravity of 2.89.

2.2 Mix Proportions

All mixes had a consistent water-to-cement ratio (w/c) of 0.45 and a volumetric ratio of 1:1.5:3

(cement: fine aggregate: coarse aggregate). At 0% (control), 10%, 20%, 30%, and 40% by weight,

GGBS was added to partially replace OPC. The mix proportions and identification labeling are

compiled in Table 1.

Table 1: Mix proportions of materials used in this study

Mix

ID

Cement

(%)

GGBS

OPC

GGBS

Fine

Agg. Coarse

Agg. Water

(kg)

(%)

(kg)

M0

100

90

80

70

60

0

350

315

280

245

210

0

525

1050

157.5

M10

M20

M30

M40

10

20

30

40

35

70

105

140

2.3 Specimen Preparation

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A revolving drum mixer was used to mix and batch the concrete for each mix. For the first two

minutes, the dry ingredients OCC, GGBS, sand, and coarse aggregates were combined. To create a

consistent, homogenous mixture, water was then added gradually while the mixture was being mixed for

an additional three minutes. Standard steel molds were used to cast the concrete samples as shown in

Figure 1. 150 mm x 150 mm x 150 mm cubes: For tests of water permeability, carbonation, rebound

hammer, and compressive strength. For split tensile strength tests, use cylinders that measure 150 mm

in diameter by 300 mm in height. For testing flexural strength, use prisms (160 mm x 40 mm x 40

mm) as shown in Figure 1. To guarantee compaction and remove air voids, all specimens were vibrated

with a table vibrator after casting. After covering the molds with plastic sheets, they were left alone for

a full day. Specimens were then demolded and moved to a curing tank where the water was kept at 23

± 2°C until they were tested at 7 and 28 days.

(b)

(c)

(a)

Figure 1: Specimen details (a) cube sample (b) cylindrical sample (c) beam sample

2.4 Testing Methods

The mechanical and durability properties were examined considering the following standard operating

procedures:

Slump Test (ASTM C143): Determined how workable and consistent fresh concrete was [10].

Compressive Strength (ASTM C39): Using a hydraulic compression machine, cube specimens were

tested at 7 and 28 days [11].

Split Tensile Strength (ASTM C496): Measured on cylindrical specimens after 28 days [12].

Flexural Strength (ASTM C78): Tested on prism specimens at 28 days using the third-point loading

method. The surface hardness of the top face of concrete cubes was measured using the rebound

hammer test (ASTM C805) [13].

Carbonation Depth: After 28 days, the color change was measured after cubes were split and a

phenolphthalein indicator solution was sprayed on them [14].

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3. Results and Discussions

3.1 Workability-Slump Test:

Figure 2 shows the slump test results; slump test results demonstrate a definite decline in workability as

the amount of GGBS increases. High workability was indicated by the control mix (M0), which had

the highest slump value of 110 mm. For GGBS-modified mixes, the slump values gradually dropped to

70 mm (M40), 80 mm (M30), 90 mm (M20), and 100 mm (M10). This decrease is explained by the

GGBS particles' finer size and larger surface area, which absorb more water and lower the amount of

free water that can flow. Umapathy et al. (2014) reported similar trends, finding that a higher GGBS

content reduced slump because of its slower early reactivity and higher water demand. All mixes

retained workable consistencies appropriate for construction in spite of this reduction.

Figure 2: Slum test results for each concrete mix made with GGBS

3.2 Compressive Strength:

Figure 3 shows how the compressive strength changed over 7 and 28 days. The control mix (M0)

reached 30.5 MPa at 7 days and 39.8 MPa at 28 days. The highest strength, with compressive

strengths of 35.2 MPa at 7 days and 45.1 MPa at 28 days, was 13.3% higher than the control M20.

Improved particle packing and initial hydration are responsible for the early-age gain, whereas the

pozzolanic reaction that forms more C-S-H is responsible for the long-term strength. Compressive

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strength dropped to 40.7 MPa and 36.2 MPa at 30% and 40% replacement levels, respectively, as a

result of slower GGBS reactivity and cementitious content dilution.

Figure 3: Compressive Strength values of each concrete mix made with GGBS

These findings support optimal performance at 20% GGBS replacement and are in line with those of

Dinakar et al. (2013) and Hussain et al. (2020).

3.3 Split Tensile Strength:

Similar patterns to compressive strength were observed in the split tensile strength results at 28 days

(Figure 4). M20 showed the highest strength of 3.92 MPa, a 14.6% increase, while the control mix

reached 3.42 MPa. At 3.75 MPa, M10 exhibited enhanced tensile strength as well.

Tensile strength decreased to 2.98 MPa (M40) and 3.25 MPa (M30) after 20%. Although lower

contents indicate inadequate hydration of GGBS (at 28 days), the improvement at 20% is attributed to

denser matrix and bond strength. Ahmad et al. The same trends were documented by (2022), who

found that the greatest compressive strength was for 15–C20% GGBS.

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Figure 4: Split Tensile Strength values of each concrete mix made with GGBS

3.4 Flexural Strength:

At 28 days, moderate GGBS contents remarkably improved flexural strength (Figure 5). M20

increased 5.42 MPa (12.4% from 4.82 MPa for M0.) This enhancement has been connected to

better matrix continuity and a more refined pore structure.

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Figure 5: GGBS Mixes showing Flexural strength at different levels

The lesser flexural strengths of 5.10 MPa and 4.65 MPa for M30 and M40 mixes respectively can be

attributed to the delayed pozzolanic reactivity and less number of available OPC. The patterns are

consistent with findings from Kannan et al. (2021), who found that GGBS produced maximum

flexural strength of 15–25%.

3.5 Rebound Hammer Test:

Figure 6 displays the surface hardness findings from the rebound hammer test. For the control mix, the

rebound number averaged 32. The mixes M10 and M20 recorded a value of 33 and 34 respectively,

reflects increased surface hardness.

Figure 6: Rebound hammer test values of each concrete mix made with GGBS

However, M30 and M40 reduced to 30 and 28 respectively, which proved the physical test results

that showed the strength decrease. These findings align with the results by Sequeira et al. As observed

by [25], incomplete hydration at higher GGBS content was linked to lower surface hardness.

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3.6 Carbonation Depth:

However, the carbonation test results (figure 7) confirm that carbonation depth was gradually

heightened with the rise in GGBS proportion. The depth was 1.8 mm for M10 and 1.9 mm for M20

while it was found to be 1.7 mm for control mix. M30 and M40 deep measured are 2.4 mm and 3.1

mm respectively. As depth increased, higher GGBS levels decreased the amount of Ca(OH)₂ available

to buffer carbonation. However, good performance was confirmed by the carbonation resistance at

20% replacement, which remained acceptable. These findings are in line with those of Habert et al.

(2020), who found that GGBS contents above 25% increased carbonation susceptibility.

Figure 7: Carbonation depth values of each concrete mix made with GGBS

4. Conclusions

The mechanical and durability properties of concrete that used 10%, 20%, 30%, and 40%

replacement levels of ground granulated blast furnace slag (GGBS) as a partial cement substitute were

investigated in this study. The results demonstrated that, when applied sparingly, GGBS can greatly

improve concrete's performance. The following are the main conclusions:

✓ Test results indicated that a 20% replacement level (M20) exhibited the most balanced and

superior performance across all parameters tested. Besides having the lowest carbonation

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depth (1.9 mm), this mix achieved the highest compressive strength (45.1 MPa at 28-day),

optimal split tensile (3.92 MPa) and flexural strength (5.42 MPa). Most of these

improvements are linked to the synergistic impact of GGBS induced microstructural

compaction and pozzolanic activity as well as a better matrix, fines pore structure, and denser

interfacial transition zones (ITZs).

✓ In contrast, due to the lower reactivity of GGBS and the lower cementitious content with

higher levels of replacement (at levels above 20%), the performance decreased (particularly at

40%). Higher replacement levels also correlate with increased carbonation depth and water

permeability, which further suggests that as slag content increases without long curing times,

limitations appear.

✓ 35% replaced with GGBS achieved structural function with lower OPC consumption

(20%>) bringing down the carbon footprint in the construction process which had an

influence environmentally.

✓ Future work, therefore, must focus on (i) long-term performance for field exposure conditions,

(ii) application of hybrid use of GGBS with other SCMs, and (iii) microstructural

characterization (SEM/XRD) for a better understanding of the observed trends in durability

and hydration kinetics. One approach to developing strong and sustainable infrastructure

systems is to blend GGBS into conventional concrete.

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