Naaem M. Al-Hantoosh*
| Harith Abdullah Ali | Sawsan Abdullah Hassan | Wisam Dheyab
© 2024 The authors. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).
OPEN ACCESS
Ground granulated blast furnace slag (GGBFS) conventionally has been mixed with ordinary Portland cement (OPC) owing to decrease the ecological impact and improve the engineering behavior. Concrete with GGBFS illustrates different strength enhancement of normal concrete, but sensitive, to environmental situation. Recently, the studies of decreasing the environmental impact of utilizing ordinary Portland cement in concrete production showed great attention. In this range, this study highlights the using of local blast furnace slag in producing cementitious material. In this paper, alkali-activated GGBFS replaced the OPC and ordinary GGBFS by ratios calculated by several compressive experiments. Compressive strength demonstrated that CB40 and CB50 have equal compressive strength as OPC. On the contrary, ACB60 showed (36%) increase in compressive strength over OPC for (28 days) curing. SEM and XRD analysis demonstrated formation of high content gels by incorporation alkali agent.
GGBFS, compressive strength, ordinary Portland cement, SEM and XRD analysis, compressive strength
Concrete is one of the most common materials consumed in construction due to its many benefits. The high cement consumption has caused an increasing of the global warming [1]. Production of OPC is one of the dominant sources for dioxide carbon emissions [2]. The cement industries consume approximately (12-15%) of the total energy consumption which used in all industries throughout the world [3, 4]. The High energy consumption is also increasing Carbon dioxide emission due to the increasing the use of cement in construct infrastructure and buildings for a higher population prompted researchers to find new ecologically friendly alternatives to cement [5-7].
Alkali activated material (AAM) (binder material) is one of the future cement replacement which appear to likeness a mechanical properties of Portland cement [8], in spite of the likeness in the mechanical properties as Portland cement, nevertheless is too early to use as replacement. AAM can be produced by adding powder form of an aluminosilicate – cab be obtained by product of other industrial or other low cost materials- with concentrated aqueous solution to be alkaline activator. Alkaline activator is usually used alkali hydroxide, silicate, carbonate or sulfate. Shi et al. [6] categorized five types for alkali-activated cement materials: Alkali-activated pozzolan cements, alkali-activated lime-pozzolan/slag cement, alkali-activated Portland blended cement (hybrid cements), alkali-activated slag-based cements, and alkali-activated calcium aluminate blended cement.
Alkali-activated cements formerly used Metakaolin, fly ash, and slag [9]. In steel production during iron formation, molten blast furnace slag quickly cools and forms glass granules [10]. POFA was mixed with rice husk ash (RHA), GGBFS, and fly ash as alomino-silicate ingredients to make geopolymer concrete [11, 12]. Kuhl introduced alkali activation in 1908, and Davidovits termed it geopolymer [13]. Poly-intensification of hydrolyzed aluminate and silicate caused the geopolymer binder's zeolitic crystalline structure [14]. In previous studies, geopolymeric gel and calcium silicate hydrate were also found together. Calcium silicate hydrate (C-S-H) was mostly generated by dissolving calcium in alkali with accessible silicates [15]. Synchronized geopolymeric gel and Calcium silicate hydrate (C-S-H) production may help fill binder voids and increase concrete's initial compressive strength. Dosage and kind of alkali activators determine gel formation and characteristics [16]. Sodium silicate (water glass) and sodium hydroxide (NaOH) were the most used geopolymer activating solutions [17].
According to Komnitsas and Zaharaki, alkali hydroxide dissolves aluminum-silicate sources, whereas sodium silicate solution works as a paste, activator, and plasticizer [18]. However, silicate solution is favored activating solution since it is available in liquid water glasses and increases polymerization reaction ratio [19]. Alkaline solutions induce enough Silicon and Aluminum atoms to form polymer particles, which poly-condense to create a solid [20]. Geopolymer binder characteristics are greatly affected by S/L and SS/SH ratios [21, 22]. To activate fly ash for geopolymerization, the solid-to-liquid mass ratio should be 3.0 [23]. However, particle form affects alkali activator mass needed for disintegration. Fly ash is better than Metakaolin for alkali activation because its spherical particle shape reduces the required liquid. Metakaolin's flaky shape increases the liquid demand. S/L (0.8) by mass is recommended for Metakaolin activation with optimal strength [24, 25]. Few studies examined Na2SiO3-NaOH ratio. The compressive strength of geopolymer concrete with low-calcium fly ash depended on the alkaline activator ratio. Their investigation found that increasing the sodium silicate to sodium hydroxide (SS/SH) ratio increased geopolymer concrete compressive strength by 28% [26]. A 2.5 mass ratio was advised, whereas Wang et al. reported 0.24 for geopolymer-based Metakaolin [27].
Ground Granular blast slag can be water-cooled to make ground granular blast slag. Slow air-quenching produces inactive crystalline combinations in BF. One ton of steel produces 300 kg of GGBFS [28, 29]. GGBFS concrete combinations reduce hydration heat, enhance concrete strength and durability, and are environmentally friendly [30]. Engineering construction often substitutes OPC with GGBFS [31, 32]. (GGBFS) has been combined OPC to reduce ecological burden and improve concrete engineering properties [33]. However, GGBFS is sensitive to curing circumstances and weak in early ages [34, 35]. Many studies have examined cement hydration to determine GGBFS behavior in concrete [12, 36]. Morrow III et al. [37] examined CO2 emissions and energy efficiency against cost analysis. Kim [16] found that high-volume GGBFS replacement up to 70% improved concrete durability and sustainability. GGBFS concrete has numerous advantages, including durability and long-term strength [38, 39], although it has poor initial strength and high shrinkage. Many research demonstrated that adding alkaline solution increases early strength, and others offered formulas for GGBFS slag concrete shrinkage [40, 15].
It must also anticipate GGBFS concrete's compressive strength, elastic modulus, creep, splitting tensile strength, and shrinkage. The combined effect of GGFBS slag and ultrafine palm oil fuel ash on geopolymer binder microstructure and compressive strength was studied [41]. Islam et al. [42] examined GGBFS and POFA geopolymeric binder mechanical characteristics. The binary mixture with low POFA and GGBS had the maximum compressive strength geopolymer binder. Previous research did not examine geopolymer activation and microstructure from POFA activation as an aluminosilicate material source [43]. This study promotes GGBFS as an eco-friendly cementitious material in concrete and other construction projects.
The study objectives include investigating of the process GGBFS and NaOH generate geopolymer binder, and the ratio of GGBFS to OPC and sodium hydroxide to water will be studied. These findings will also illuminate geopolymer binder's process and microstructure. This study may encourage further research on GGBFS geopolymer mortar and concrete behavior, as well as make concrete more environmentally friendly by reducing energy use and CO2 emissions. This study examined hardened geopolymer binders' mechanical characteristics, microstructure, and oxides using SEM-EDS and XRD.
2.1 Materials
2.1.1 Cementitious materials
Two types of binder materials were used in this study ordinary Portland cement OPC and Ground granular blast furnace slag. GGFBS was used in this study had fineness of 4485 cm2/gm and density 2.94 g/cm3. GGBFS was according to ASTM C 989-18 [44]. OPC was accordance with ASTM C150 [45]. Chemical composition of GGBFS and OPC were determined by (XRF) test X-Ray Fluorescence. All main chemical composition and physical properties were showed in Table 1.
Table 1. Physical properties and chemical compositions of OPC and GGBFS
|
Sample |
Surface area (cm2/g) |
Density (g/cm3) |
Ig.loss (%)* |
Chemical Compositions |
|||||||
|
SiO2 |
CaO |
Al2O3 |
Fe2O3 |
MgO |
SO3 |
MnO |
TiO2 |
||||
|
OPC |
3518 |
3.15 |
1.2 |
21.78 |
63.53 |
5.37 |
3.26 |
1.67 |
2.47 |
|
|
|
GGBFS |
4345 |
2.92 |
0.35 |
34.36 |
44.31 |
14.34 |
0.62 |
4.24 |
0.34 |
0.24 |
0.74 |
2.1.2 Alkaline activator (AA)
Sodium hydroxide was used as alkali activators in this study. The purity of used sodium hydroxide was 99% with a concentration of 10 M. Then, NaOH powder was added to solution by mixing powder with water and left for one day to decrease the temperature of reaction before using in casting of samples in this study.
2.1.3 Fine aggregate (FA)
The fine aggregate was used in this investigation was sand with graded distribution in accordance to ASTM C778 [46] as shown in Table 2. Sand had specific gravity of 2.45 g/cm3 and fineness modulus 2.01.
Table 2. Sieve analysis of sand
|
Sieve Size (mm) |
1.18 mm (No. 16) |
600 μm (No. 30) |
425 μm (No. 40) |
300 μm (No. 50) |
150 μm (No. 100) |
|
ASTM C778 |
100 |
96-10 |
65-75 |
20-30 |
0-4 |
|
Passing Grade |
100 |
98 |
72 |
26 |
3 |
2.2 Mix proportions and mixing procedure
The experimental work in this research was conducted three main steps of works study. In step-1, preparing reference cement mortar by using traditional concrete materials (cement 557.2 kg/m3, water-cement ratio 0.48, and sand/cement of 2.75with respect to ASTM C109 [47]. In Step-II, the main step focused on studying the properties of cement mortar after replacing OPC by GGBFS and selects the suitable percent of GGBFS. Step-III concentrated on additional enhancing of replacing mix water by alkali activator sodium hydroxide NaOH on the mortar of step-II, the mix proportions and mixing procedure of alkali activator sodium hydroxide NaOH according to [21]. In order to study the effect of addition of granular blast furnace slag and alkali activators, Sodium Hydroxide to cement mortar, seven different mortar mixtures (the mix proportions and mixing procedure of were presented he combined effect of GGFBS slag on geopolymer was studied [41]). Two types of cementitious materials OPC and GGBFS are used with three different cement replacement levels of 40%, 50%, and 60% were considered for GGBFS. Using Alkali activator as liquid Martials for mixing dry cement mortar with 40%,50%, and 60% OPC to GGBFS replacing ratio (see Table 3). mass of GGBFS was kept under to 20% In all mixes of present study mixtures to give satisfactory mechanical properties and workability [48]. Alkali Activator NaOH was prepared by adding water to dry powder 24 hours before casting the cement mortar. The mixing process included mixing different dry binder materials for 1 minutes after that adding water or AA (NaOH solution) and mixing for other 3*4 minutes for consistency and at last casting in mold for 7 and 28-days compressive strength.
Table 3. Proportion of mortar mixture
|
Mortar |
Cement (Kg/m3) |
Liquid/binder |
GGBFS/OPC |
Water (L/m3) |
Sand (Kg/m3) |
GGBFS (Kg/m3) |
Alkaline (10M NaOH l/m3) |
|
OPC |
557.2 |
0.48 |
- |
267.46 |
1806 |
- |
- |
|
CB40 |
334.32 |
0.48 |
0.4 |
267.46 |
1806 |
222.88 |
- |
|
CB50 |
278.6 |
0.48 |
0.5 |
267.46 |
1806 |
278.6 |
`- |
|
CB60 |
222.88 |
0.48 |
0.6 |
267.46 |
1806 |
334.32 |
- |
|
ACB40** |
334.32 |
0.48 |
0.4 |
- |
1806 |
222.88 |
267.46 |
|
ACB50 |
278.6 |
0.48 |
0.5 |
- |
1806 |
278.6 |
267.46 |
|
ACB60 |
222.88 |
0.48 |
0.6 |
- |
1806 |
334.32 |
267.46 |
3.1 Compressive strength
Compressive strength of all samples were done in different ages 3, 7, and 28 days for (50*50*50mm) mortar cube according to ASTM C109 [47]. The GGBFS effect on the compressive strength of cement mortar can be showed in Table 4. Each value represents the average of three compressive strength test as a result. Increasing the alkali in the mixture ACB60 led to a decrease in the reaction water which reduced the hydration process of ordinary Portland cement OPC and thus led to a reduction in gel formation. Responsible for increasing the compressive resistance. Also, increasing the alkaline solution by GGBFS slag led to exceeding the optimum reaction ratio and a decrease in the required reaction ratio occurred, which led to a decrease in the compressive strength.
Table 4. Compressive strength
|
Sample |
Compressive Strength (Mpa) |
||
|
3 Days |
7 Days |
28 Days |
|
|
OPC |
32.08 |
38.48 |
40.91 |
|
CB40 |
31.10 |
37.63 |
40.34 |
|
CB50 |
30.68 |
36.57 |
39.70 |
|
CB60 |
25.52 |
30.61 |
33.57 |
|
ACB40 |
39.27 |
47.12 |
52.84 |
|
ACB50 |
42.03 |
52.34 |
56.03 |
|
ACB60 |
35.40 |
43.11 |
46.15 |
3.2 Mineralogy and microstructure
3.2.1 XRF test
The chemical compositions of all mortar types are determined by (XRF) test X-Ray Fluorescence (see Table 5).
Table 5. Chemical composition of mortar by XRF test
|
Sample |
SiO2 |
CaO |
Al2O3 |
Fe2O3 |
MgO |
SO3 |
MnO |
TiO2 |
K2O |
|
OPC |
34.38 |
30.38 |
2.906 |
3.08 |
1.646 |
1.073 |
0.095 |
0.285 |
0.438 |
|
CB40 |
47.01 |
18.27 |
1.938 |
3.564 |
0.849 |
5.329 |
0.248 |
0.206 |
0.443 |
|
CB50 |
44.02 |
18.11 |
2.113 |
4.194 |
1.003 |
5.965 |
0.299 |
0.221 |
0.373 |
|
CB60 |
40.07 |
20.20 |
2.245 |
4.741 |
1.073 |
6.542 |
0.354 |
0.204 |
0.3624 |
|
ACB40 |
24.74 |
21.14 |
1.991 |
3.371 |
1.151 |
6.138 |
0.240 |
0.2003 |
4.404 |
|
ACB50 |
34.93 |
20.79 |
2.138 |
4.737 |
1.024 |
5.530 |
0.355 |
0.201 |
4.804 |
|
ACB60 |
32.34 |
18.73 |
2.1 |
4.411 |
1.084 |
5.629 |
0.331 |
0.225 |
6.51 |
3.2.2 XRD
Figure 1a and 1b present the XRD of sand-(50%)GGBFS-(50%)cement and sand-(60%)GGBFS-(40%)cement mixtures treated with 10 M of NaOH after 28 days of curing. Peaks of quartz, brucite, kaolinite, serpentine, sodium silicate (Na2SiO3) and mullite are defined as a result of olivine dissolution through the sodium hydroxide in soil. Peaks of quartz (SiO2) (9, 24, 26, 28, 39, and 45°), brucite (18, 21, 36, and 48°), and sodium silicate (30 and 35°) were detected throughout the patterns [48, 49]. The figure shows the XRD analysis of 20% olivine-treated soil after 12, 48, and 168 h of carbonation under 200 kPa. Increasing carbonation periods led to a decrease in the brucite and magnesium peaks, whereas nesquehonite peaks increased as result of the carbonation process.
(a)
(b)
Figure 1. XRD of (a) ACB50; (b) ACB60
3.2.3 SEM
Figure 2a shows the microstructure of sand cement mortar. Figure 2b presents sand-(40%)GGBFS-(60%)cement mixture. Figures 2c and 2d present sand-(50%)GGBFS-(50%)cement and sand-(60%)GGBFS-(40%)cement mixtures treated with 10 Molarity of NaOH after 28 days of curing. Figure 2a demonstrates that the morphology of sand cement mortar consists of groups of connected particles, whereas the clustery particles seems more connected for sand mixed with (40%) GGBFS and (60%) cement in Figure 2b. Figure 2c clarifies the sand-cement-GGBFS treated mixture after curing. By making a comparison of Figures 2a and 2b with Figures 2c and 2d, it shows how alkali-activated treatment gives a more dens mass, and fills the voids of the sand with gel as a result of GGBFS decomposition and precipitation. Thus, SEM images reveal a dens morphology with few or no gaps, which is stable with the mechanical properties illustrated. Figures 2c and 2d evidence the existence of a new amorphous phase, which show the formation of a gels material surrounding sand particles.
(a)
(b)
(c)
(d)
Figure 2. SEM images of (a) OPC (b) CB40 (c) ACB50 (d) ACB60
The compressive strength test results of OPC, CB40, CB50, CB60, ACB50, and ACB60 slag concretes and alkali-activated slag concretes were assessed to test the probability of using GGBFS slag as a cementitious material. Based on the previous results, the following conclusions can be made:
1. The properties of fresh concrete were examined by measuring the compressive strength and the particle morphology were examined by XRD and SEM analysis. The cement content in the mixtures were substituted by GGBFS. Compressive strength tests showed that CB40 and CB50 reflected the highest compressive strength in (28 days).
2. Selected GGBFS contents (CB40, CB50 and CB60) were alkali-activated. Compressive tests of (ACB50 and ACB60) demonstrated an increase in compressive strength with time.
3. SEM and XRD of ACB50 and ACB60 showed increase in gel content with activation time increase. As a consequence, compressive strength of ACB50 and ACB60 showed highest values.
4. Based on SEM and XRD results analysis, we could confirm the reaction characteristics of ground granulated blast furnace slag. Major reaction products were found to be calcium silicate hydrate gel and Ca (OH)2.
5. The researcher suggests for future work to study the effect of high temperatures on the mixtures that were used in the current study.
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