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. 2023 Mar 28;16(7):2684.
doi: 10.3390/ma16072684.

Calcined Clays from Nigeria-Properties and Performance of Supplementary Cementitious Materials Suitable for Producing Level 1 Concrete

Abubakar Muhammad  1 , Karl-Christian Thienel  1 , Sebastian Scherb  1
Affiliations

Calcined Clays from Nigeria-Properties and Performance of Supplementary Cementitious Materials Suitable for Producing Level 1 Concrete

Abubakar Muhammad et al. Materials (Basel). .

Abstract

In this work, four naturally occurring (two kaolinite-rich and two smectite-rich) clay samples were collected from different areas around the Ashaka cement production plant, located in Gombe State, Nigeria and calcined in a laboratory. The mineralogical characterization of the clays was carried out by XRD. The hydration kinetics of the calcined clay-cement systems were monitored by isothermal calorimetry. Workability was determined using the flow table method. The reactivity of the calcined clays was determined from the solubility of Si and Al ions and the strength activity index. All calcined clays studied met the requirements of ASTM C618 for the use of natural pozzolans as a partial replacement for hydraulic cement. The metasmectite clays yielded a higher specific surface area, increased water demand, and less reactive Si and Al ions compared to the metakaolin clays. The two calcined clay groups require the addition of superplasticizer to achieve a workability class similar to the Portland cement mortar system. They can be used to replace Portland cement at replacement levels of up to 45%, in combination with limestone powder to form an LC3 cement, thereby achieving at least a "Level 1" reduction in greenhouse gas emissions.

Keywords: calcined clay; clay mineralogy; hydration mechanism; ion solubility; metakaolin; metasmectite; strength activity index; workability.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Map of Nigeria obtained from [42]. The location of different cement plants and of the sampling sites are added.
Figure 2
Figure 2
Differential thermal analysis (a) and mass loss (b) of the raw clays.
Figure 3
Figure 3
XRD patterns of the NRC: K—kaolinite, S—smectite, Q—quartz, M—mica, I—illite, and G—gypsum. The y-axes are shifted in the cases of NRC-1, 2, and 4 (the maximum shift for NRC-1 was 1000 counts).
Figure 4
Figure 4
Si and Al ion solubilities of the CC.
Figure 5
Figure 5
Influence of CC and LP on the flow spread of the mortar: (a) 20 vol.% CC + 80 vol.% OPC; (b) 30 vol.% CC + PLC.
Figure 6
Figure 6
SAI of the mortars: (a) 20 vol.% CC + 80 vol.% OPC; (b) 30 vol.% CC + 15 vol.% LP and 55 vol.% OPC. The numbers placed above the bars denote the compressive strength value in MPa, approximated to the nearest whole number.
Figure 7
Figure 7
SAI of the NCC mortars compared to PLC mortar mixes. The numbers placed above the bars denote the compressive strength value in MPa, approximated to the nearest whole number.
Figure 8
Figure 8
Heat flow of OPC-20NCC (a) and of OPC-15LP-30NCC (b) systems.
Figure 9
Figure 9
Heat flow of the OPC-15LP-30NCC systems with 5 wt.% G.
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