1 Introduction

The demand for this OPC has increased extensively over the last few decades as it is the key to industrial development and modernization [1]. Global cement consumption has increased significantly over time due to growing demand in the construction industry. More than 10 billion cubic meters of concrete are produced annually around the globe, and it is unlikely that this volume will recede [2]. To produce OPC, calcination at a temperature around 1300 °C using coal or petroleum as fuel is necessary, which uses up a lot of fossil fuel and raises the cost of production [3]. The use of cement for the construction of infrastructure has been hampered in several developing nations by the high cost of cement production [4]. Overall, there are numerous issues that the worldwide cement production business is currently dealing with, including a lack of resources, excessive energy use, and environmental contamination [5,6,7,8,9].

The UN Environment Program estimates that up to 41% of the world’s anthropogenic carbon emissions come from buildings. Due to the enormous demand for concrete, the cement industry is responsible for 5–8% of the world’s greenhouse gas emissions [10]. Concrete is the second most treated material in the world after water. Urban planning as a whole has an impact on potential infrastructure and public transportation, social resilience (via community building), and climate resilience solutions (e.g., resilience against flooding, earthquakes, and heat islands).

In the previous two decades, the cement industry has seen some major capacity expansions in anticipation of the country’s growing cement demand. The sector’s players have recently been encouraged to expand by promising demand prospects from the government of Pakistan initiatives such as the Naya Pakistan Housing Program (NPHP), development of dams, and China Pakistan Economic Corridor (CPEC) related operations [11]. However, while production of clinker, a significant amount of carbon dioxide emits.

In Pakistan, there are 24 cement plants in operation, with over twelve in Punjab, five in KPK, two in Baluchistan (for a total of 19 in the North Zone), and five in Sindh (Southern zone). The Pakistani government has issued numerous No-Objection Certificates (NOCs) for the installation of cement plants in response to the rising demand for cement. Four factories are located in Mianwali, one in Pind Dadan Khan, two each in Taxila and Dera Ghazi Khan, and seven in other parts of the country. Three of the sixteen facilities are currently under construction and will be completed and operational by the end of the year. Along with the limestone range from the Salt Range to Kalabagh, Taxila-Karak-Kohat, and DG Khan these new plants are being constructed. All Pakistan Cement Manufacturers Association (APCMA) records indicate that the industry shipped 4.74 Mt of domestic cement in March 2022, up from 4.56 Mt in March 2021, a 4.02% rise. A yearly overview of the fiscal year (2019–20), the production capacity of Pakistan to produce cement is 63.6 million tons, and the total dispatches reported that year was 47.8 million tons. It shows the capacity utilisation of cement is 75.1% [12].

The cement sector in Pakistan is expanding steadily and moving in the right direction. Pakistan’s cement industry has a bright future as all signs point to a positive path for the sector [13]. Cement output is directly proportional to a country’s population because as the population grows, so does the need for additional housing. According to the State Bank of Pakistan, Pakistan has a housing shortage of 12 million homes. As a result, the production of cement drastically increases. The exponential regression method [14], predicts that Pakistan will have roughly 276.5 million people living there in 2030. It is anticipated that 77.492 Mt of cement will be produced for a population of 276.5 million.

Pakistan’s CO2 emissions per capita are still modest, but energy-related emissions have increased. Cement industries are the primary source of air pollution in Pakistan, with CO2 being the primary pollutant, causing havoc on the environment. Fuel combustion (to heat limestone, clay, and sand to 1450 °C) is the source of CO2 emissions in cement manufacture. Between 2000 and 2015, the impact of cement manufacturing on CO2 emissions increased by 5–10%. By 2028, the globe is on track to exceed CO2 emissions, resulting in a more than 1.5 °C rise in global warming compared to pre-industrial levels [15].

As of today, no greenhouse emission penalties are applied to cement industries in Pakistan. However, the time is near, when the cement industry may face penalties over carbon footprints. To incorporate the demands of cement sustainably, few cement industries in Pakistan are utilizing fly ash and limestone up to 5% as performance improvers [16]. But, the scarcity of good quality fly ash and high clinker replacement with limestone remains an issue for the manufacturers. High replacement of clinker with limestone has its own challenges.

The use of calcined clay as SCM is a more sustainable approach due to its accessibility and economic factors. This blend of cementitious material offers almost the same or better physical properties than OPC. Limestone is included with calcined clay to reduce the amount of clinker in cement, and its composition consisting of 50% clinker content, 30% calcined clay, 15% raw gypsum, and 5% gypsum. It is also known as Limestone Calcined Clay Cement (LC3). LC3 has several benefits, and it’s more durable than OPC [17]. However, compression and durability testing revealed that the clay with a 40% kaolinite content was superior to all other LC3-50 blends. A recent study conducted in Pakistan by Sheikh et al. demonstrated the potential for LC3 to serve as a substitute for OPC and reduce carbon footprints without compromising mechanical properties and durability performance [18].

Clay is found to have the potential of being used as a substitute for conventional cement raw materials. However, not all types of clay qualify for the purpose, only clays having kaolinite content of 40% or above possess the properties to be used without having any effect on the hydration and strength of cement, and ultimately replacing cement clinkers which are the main source of CO2 emission, ultimately resulting in reducing the CO2 emission up to 40%.

This paper identified the mineral properties and kaolin content of 39 clay samples from all over Pakistan and tests the reactivities of calcined clays using an XRD and TGA. This study will be beneficial for using these clays in Pakistan’s cement industry in the future.

2 Topography of Pakistan

Pakistan has a unique topography and a diverse range of mountains that contain a variety of minerals. Pakistan has 13 mountain ranges (Fig. 1a) that are rich in minerals such as limestone, gypsum, clay, iron, and copper. The salt range, the Koh-e-Sulaiman range, and the Khirthar range all have a lot of different types of clay in several formations based on the soil or rock type of the location. Various types of clay, such as bentonite, china clay, and fire clay, can be found in different parts of Pakistan (Fig. 1b). The alteration of feldspars produces China Clay [19]. It was found in the areas of Dhed Vero, Parodhoro, Karkhi, Dungri, Motijo, Vandio, Ramji-jo-Vandio, and Didwa-Surachand [20]. Fire clay is resistant to shrinkage, abrasion, and corrosion under high temperatures and withstands thermal spalling. Punjab is the world’s largest producer and consumer of fire clay. The main production areas are Mianwali, Sargodha, Attock, and D.G. Khan. These are leftover sedimentary deposits found in the Salt Range’s Indus Formation. Bagh, Choi, and Surge are the primary deposits. Large amounts of clay can be found at Manhiala, Wehali, Nali, and Dalwali, where the clay is found at the base of the Paleocene Hangu Formation in the Indus Formation. It’s found at the top of the Tobra Formation at Ara, near Khewra. It is also found in the form of underclay linked with the Dandot coal seam at Karauli and Ratucha. Several of these deposits are now being mined.

Fig. 1
figure 1

Topography of Pakistan. a The Mountain ranges of Pakistan contain a variety of minerals. b Potential areas of various types of clay deposits

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In the western Salt range, the second horizon is found in Jurassic Datta Formation, and the principal deposits are Dhak Pass, Manza Bazar, Chabil, Dama, and Gole Wali. Fire clay can be found at Isa Khel in the Trans Indus Salt Range [19]. Pakistan’s total fire clay deposits are estimated to be around 100 Mt. The majority of current output comes from the Mianwali and Sargodha deposits, which are heavy load refractory clay. It is mostly utilized in cement and other industries for furnace lining. It’s also found in the D.I. Khan District. Many coal layers in the Sulaiman fold belt are connected with the fire clay beds. Ochre, limonite, iron, and fire clay from the Chitarwata, Rakhi Gaj, Vitakri, and Drazinda formations, as well as the Vihowa group in the northeastern Sulaiman fold belt, appear to be significant. Clay deposits can also be found in Azad Kashmir’s Nammal, Sakesar, Chorgali, Kuldana, and Murree formations. Dir, Hazara, and Gilgit also have smaller deposits.

3 Materials and methods

3.1 Geographical distribution of clay materials

Study the specifics of Kaolin’s prior reports and prospective locations. Then, these locations are examined using the available documentation and reviews from specialists in the department of minerals and mines and the Geological Survey of Pakistan. The initial stratigraphic selection of sites is carried out using the geobotanical approach, in which the interpretation of the plant cover enables the detection of changes or plant associations characteristic of specific types of geologic settings or mineral deposits within these habitats. The location of Pakistan’s clay resources is shown in Fig. 2, demonstrating the country’s potential clay reserves. For this research, 39 clay samples from all around Pakistan were collected. Table 1 lists the districts and geographic location data for the clay sampling sites.

Fig. 2
figure 2

Potential clay sites in Pakistan. The locations of the clay sample collection sites

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Table 1 Geographic location information of collected clay samples
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3.2 Material preparation

Raw clay was first dried in a 100 °C oven for 24 h. Subsequently, the clay was pulverized using a ball miller, and particles up to 75 µm were retained for further analysis, including XRD, TGA, and XRF tests, as shown in Fig. 3.

Fig. 3
figure 3

Presents the particle size distribution of eight selected samples with a kaolinite content exceeding 40%, as analyzed in detail

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3.3 Characterization

X-ray diffraction was used to determine the mineral compositions of the clay samples (XRD). An Empyrean 4 kW diffractometer (PANalytical) with a PIXcel detector and a Cu-K X-ray source was used to capture the XRD images. The setpoints for the voltage and current were 60 kV and 60 mA, respectively. By using powder diffraction on samples up to 75 µm, the full mineralogy was identified. The range of the XRD pattern was 5° to 60°.

A STA449F3 thermogravimetric analyzer (NETZSCH) was used to perform the thermogravimetric (TG) analysis. The analysis was carried out at a temperature increase rate of 5 °C/min between ambient and 1000 °C. N2 was the atmosphere, flowing at a rate of 20 mL/min. Based on the mass loss \(({m}_{loss})\) between 400 and 600 °C using the TG tangent method, the kaolinite content was calculated [21]. As a result, the kaolinite content \({m}_{k}\) was determined using:

$${m}_{k}={m}_{loss}\times \frac{{M}_{K}}{2{M}_{water}}$$
(1)

where \({M}_{k}\) is the molar mass of kaolinite in its ideal chemical formula (i.e. 258.16 g/mol), and \({M}_{water}\) is the molar mass of water (i.e. 18.02 g/mol).

The Elemental analysis method can determine the class of alumino-silicates present in a material, and this approach has been consistently used for this purpose in clay analysis [22]. The parental clays were found to contain significant amounts of SiO2 and Al2O3 in kaolinitic clays.

The pozzolanic reactivity of calcined clay was evaluated using the R3 reactivity test [23] in the Isothermal Calorimeter HPC I-Cal 2000. The sample was prepared with the ingredients listed in a Table 2. Clay samples calcined at 800 °C in a furnace for an hour. Then, 10 g of paste was then placed in the Isothermal Calorimeter at 40 °C for 7 days, during which the total heat generated was measured.

Table 2 The proportion of the mix design for the R3 reactivity test sample paste
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4 Results and discussions

Previous study shows that XRD quantification of kaolinite is challenging due to its structural characteristics, including extensive layer disorder and preferred orientation. Therefore, TGA is a preferable alternative for this purpose [24]. In this study, to determine the kaolinite concentration as per Eq. (1), the mass loss in the 400–600 °C temperature range can be identified using the TG tangent method. As a result, Table 3 shows the kaolinite content of the 39 samples.

Table 3 Kaolinite content of the samples collected from different districts
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4.1 Thermal properties

The DTA curves of the kaolin samples demonstrate that the first dehydration-related endothermic event, or loss of adsorbed water, is detected between 150 and 250 °C (Fig. 4) [25]. A well-defined endothermic peak in the DTA curve at 500–550 °C is connected to the second endothermic peak, which represents the dehydroxylation of kaolinite [26,27,28].

Fig. 4
figure 4

TG-DTG curves of various samples. The graphs Indicate the endothermic peak associated with kaolinite’s dehydroxylation. a Sample PK-01 b Sample PK-11 c Sample PK-14 d Sample PK-30 e Sample PK-29 f Sample PK-03 g Sample PK-04 h Sample PK-07, which contains kaolinite to varying degrees (74%, 18%, 60%, 90%, 88%, 29%, 53%, and 43%)

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The weight loss in the temperature range of 500–600 °C is due to the dehydroxylation of pure kaolinite, whereas the minor mass loss in the region of 30–200 °C can be attributed to the loss of absorbed water. Endotherms at temperatures between 500 and 600 °C demonstrated the breakdown of hydroxyl ions from kaolinite, which changed the environment from octahedral coordination in kaolinite to tetrahedral coordination in metakaolin, which then crystallized either directly to mullite or first to Al-Si-type spinel and then nano-size mullite (3Al2O3.2SiO2) [29]. Previous studies show that the weight loss in this temperature indicated by the TGA curves ranges from 7.04 to 8.48%, considering that pure kaolinite loses 14% of its weight because of dihydroxylation [30].

As shown in Fig. 4, at 400–600 °C, the mass loss was larger for the PK-01, PK-14, PK-30, PK-29, PK-04 and PK-07 samples while it remained relatively stable or decreased less for the PK-11 and PK-03 samples, indicating that the PK-01, PK-14, PK-29, PK-04, PK-07 and PK-30 samples contained more kaolinite than the other samples. The thermogravimetric plots for sample PK-11 and PK-03 have an earlier dramatic downward slope than the other samples (Fig. 4b & f). This could be due to two different factors: the first is related to the arrangement and structure of kaolinite [31], and the second is the dehydration of the hydrate phase, which is associated with hematite in natural soil [32]. The kaolinite concentration of the clay samples as determined by the tangent method is shown in Table 3 above.

4.2 Mineral composition of the clay materials

XRD analysis of the 39 clay samples revealed that various clay samples did not contain the same mineral phases. The XRD spectra of eight representative samples, PK-1, PK-11, PK-14, PK-29, PK-03, PK-04, PK-07, and PK-30, which contain all the mineral phases in the 39 clay samples, are shown in Fig. 5 to clearly illustrate the clay samples. The spectra reveal that the composition of clay’s mineral phases is compatible with that of aluminium silicate hydrates and quartz peak, which is comparable to both common clay and kaolinite clay. The composition of PK-11 is slightly different and includes both zeolite and quartz (Fig. 5b). This is probably the cause of its low kaolinite content. PK-01 and PK-14 have kaolinite as their primary mineral (Fig. 5a & c). Furthermore, the high kaolin content clay PK-30 (Fig. 5d) contains nacrite minerals. An unusual kind of kaolinite called nacrite is amorphous but chemically identical to kaolinite [33]. This high kaolinite content in clay may be due to the presence of the mineral nacrite. Kaolinite and diaspore minerals can be found in samples PK-29 (Fig. 5e). Diaspore is a mineral composed of aluminum oxide hydroxide. It might be a reason of high kaolinite content in the clay. Both kaolinite and quartz are included in the mineral composition of PK-03 and PK-04 (Fig. 5f & g). Kaolinite and silicon oxide minerals are present in PK-07 (Fig. 5).

Fig. 5
figure 5

XRD spectra of different clay samples. The spectra show the mineral phase composition of clay. a Kaolinite mineral dominates sample PK-01. b Zeolite and quartz minerals are present in sample PK-11. c Sample PK-14 also contains kaolinite mineral. d Sample PK-30 has nacrite mineral in its composition. e Kaolinite and Diaspore minerals are present in sample PK-29. f & g Sample PK-03 & PK-04 contains kaolinite and quartz minerals. h Kaolinite and silicon oxide minerals are present in Sample PK-07

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4.3 X-ray fluorescence characterization

In order to gain a more detailed understanding of the clay samples under investigation, XRF analysis was performed on a subset of eight specimens selected from the initial pool of 39. Interestingly, the results showed that seven of these samples contained over 40% kaolinite, while PK-11 had a comparatively low kaolin content of only 18%.

Among the eight selected samples, the silica content ranges from 65.39% to 18.36% from Table 4. Ideally, kaolin clay contains 46.6% silica [34]. However, two samples, PK-29 and PK-30, deviate from this range while still having a high kaolin content. Previous studies showed that the intensity of kaolinization depends on the Al2O3 content, and lower Al2O3 content indicates incomplete kaolinization [35, 36]. Therefore, PK-29 and PK-30 are rich in kaolinite due to their abundant aluminous content. From these results, it can be observed that rich kaolin clay has a higher aluminous content compared to silica.

Table 4 Composition of clay samples based on XRF (weight %)
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The ferrous content ranges from 0.45–2.31%, except PK-14, which has 10.88%. PK-14 holds a substantial amount of ferric oxide, accounting for 10.88% of its composition and from Fig. 6, it’s clear that PK-14 has the darkest colour among all clays. While the presence of Fe2O3 is a significant factor in determining the colour of clay, it is not the only constituent that affects the colour. CaO, MgO, TiO2, and MnO2 are other elements that can significantly modify the colour of the clay [37]. Therefore, it is essential to consider all these constituents when trying to achieve a specific colour.

Fig. 6
figure 6

Images of eight clay samples with kaolin content above 40%, except PK-11, were collected from different locations and were analyzed using X-ray diffraction to confirm their chemical composition

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The colour of calcined clay was observed to range from grey to different shades of red and is considered a challenge for the widespread adoption of LC3 cement. Additional research is necessary to comprehensively understand how the colour of clay influences the heat of hydration, mechanical properties, and durability performance of LC3 [38].

4.4 Reactivity test

Two clay samples, PK-07 and PK-11, which have a kaolin content of 43% and 18%, were selected for the test. This test aimed to determine the reactivity of the clay samples. According to the reactivity test results shown in Fig. 7, PK-7 and PK-11 produced different amounts of normalized total heat per gram of clay. Specifically, PK-7 released 393.75 Joules per gram of clay, whereas PK-11 only generated 212.86 Joules per gram. The result suggests that the kaolin content in the clay has an impact on its reactivity, with higher levels of kaolin leading to greater reactivity. Overall, this test provides valuable insights into the factors that influence the reactivity of clay.

Fig. 7
figure 7

Heat release of calcined clay through R3 test

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5 Conclusion

In this study, a field investigation was used to explore an indicative geographical distribution of Pakistani clays used as supplementary cementitious material. Clays were collected from several locations. The particles with a size up to 75 µm were taken as samples after the raw clays were dried and ground. Clay samples’ mineral and thermal characteristics were identified using XRD and TGA, respectively.

  1. 1.

    As indicative peaks in XRD graphs shows rich kaolinite minerals in collected clay samples. Other rich kaolinite minerals like nacrite are also present in clay which is the reason for the high kaolinite content in clay samples of Pakistan.

  2. 2.

    The phase transformation temperatures determined for local kaolin clays were found consistent with previous studies; however, no systematic endothermic dips were observed at ~ 150 °C, probably due to the use of oven-dried samples. The range of kaolinite content is 1.44 − 89.69% as calculated by the TG tangent method.

  3. 3.

    XRF analysis revealed that the clay samples had different levels of kaolinite, silica, and ferrous content. The aluminous content affects kaolinization, while ferric oxide affects clay color.

  4. 4.

    The reactivity test on two clay samples with different kaolin contents showed that higher kaolin content led to greater reactivity. PK-7 had a higher kaolin content and generated more heat than PK-11. This test provides important information on the factors that affect clay reactivity.

This research shows that Pakistan has potential kaolinitic clay reserves. This type of clay prospect is to be used as SCM in the production of cement. Due to the availability of abundant clay reserves, it is feasible for Pakistan to produce a new type of ternary cement blend named Limestone Calcined Clay Cement (LC3). As has been previously discussed, some locations meet the requirements for the amount of 40% kaolinite content, and these locations are also close to the active cement plant. However, it was recommended to manufacture LC3 cement with clay that had a 40%–75% kaolinite content [39]. The samples PK-30 and PK-29 are 14.2 km apart from Askari cement Nizampur and contain up to 90% kaolinite. As of June 2020, it had two production lines and produced 1,701,500 tonnes of cement annually [12]. The distance between the sample PK-14 and the Bestway cement plant is 10.2 km, and the sample contains up to 60% kaolinite. Additionally, Bestway Cement Limited—Kallar Kahar has two production lines with a yearly capacity of 3,600,000 tonnes [12]. The location of sample PK-14 is also close to D. G. Khan Cement, Kallar Kahar, Chakwal (17.9 km distant). The samples PK-01, 04, 07, 05, and 06 all exhibit kaolinite contents that are greater than 40%, enabling it to synthesize LC3 from these resources. These locations are in Mianwali. These sites are nearby (15.6 km), at Maple Leaf Cement Factory Limited—Daudkhel. It has three production lines and a yearly output capacity of 5,670,000 tonnes of cement [12]. In Mianwali, Bestway Cement Limited is also building a new facility. It is conceivable for all of these cement manufacturing facilities to generate LC3 instead of OPC. If we start using LC3 instead of Portland cement, we will be able to reduce CO2 emissions and improve our environment.