Malawi is one of the least-developed countries in Sub-Saharan Africa with disaster-prone housing infrastructure characterized by poor construction materials. Therefore, there is a need to provide resilient and cost-effective materials, such as limestone calcined clay cement (LC3). However, the exploitation of LC3 in Malawi is limited due to a lack of mineralogical information about the clays and limestone and related strength and durability when used as a cementitious material. In this study, the strength and physico-chemical properties of LC3 systems with 50% and 40% clinker contents (LC3-50 and LC3-40) were investigated. Cement mortar specimens were prepared at water to cement (w/c) ratios of 0.45, 0.5, and 0.6 with varying calcined clay (CC) to limestone (CC/LS) ratios (1:1, 2:1, and 3:1). The effects of CC/LS ratio on the fresh properties, strength, and durability were investigated. The results showed that specimens with 40% Portland cement replacement levels (LC3-40) exhibited higher standard consistency (up to 45%) than LC3-50, porosity in the range of 8.3–13.3%, and maximum water uptake in the range of 3.8–10.9%. On the other hand, LC3-50 samples offered the highest strength of approximately 40 MPa, complying with requirements for pozzolanic cementitious materials, whereas LC3-40 conforms to the strength requirements for masonry cements. This work shows that LC3 systems can be manufactured with local clays and limestone available in Malawi, and used as a sustainable construction material to mitigate carbon emissions as well as boost the local economy.

Malawi is located within the southern branch of the active East African Rift System, where earthquakes of moment magnitude (M_w) 7.0 or greater can occur along major faults. The majority of dwellings in the country are non-engineered unreinforced masonry constructions, built by local artisans with little input from engineers. These constructions are highly vulnerable to seismic events due to poor-quality materials and lack of construction detailing. This study presents a new methodology to assess the seismic fragility curves of typical dwellings located in the Central and Southern Malawi. On-site inspections of buildings are carried out to assess geometrical and structural features of 646 façades, and an experimental campaign is performed to characterise the mechanical properties of local construction materials. The collected data allow the identification of different building typologies in terms of quality of materials and construction techniques. The critical failure modes for each of the inspected façade at their ultimate limit state are evaluated analytically. Damage limit states are defined and adopted to derive simplified Static Push-Over (SPO) curves, transformed into incremental dynamic analysis (IDA) curves by using SPO2IDA. The IDA curves are then used to obtain fragility curves for the specific damage limit states. The fragility curves presented herein are the first to be calculated for these building typologies, based on local data, and unfortunately, they show that buildings in Malawi are far more vulnerable to earthquakes than estimated from previously available international reference data. The fragility curves developed in this study may prove useful for assessing the seismic risk of these building typologies in Malawi and other East African countries.

Research on the combined substitution of supplementary cementitious materials (SCMs) has already demonstrated that it might be one of the few viable options to produce low-carbon concrete at scale. This paper presents an experimental investigation on the performance and durability of rice husk ash (RHA) and calcined clay (CC) in ternary blended concrete exposed to chloride attacks under wet/dry cycles. Portland cement (PC) was replaced by RHA and CC up to 50% by weight to produce low-carbon concrete. Samples were subjected to wet/dry cycles in 3.5% NaCl water, with mineralogical composition and microstructure development before and after exposure analysed by TGA-DSC, MIP, XRD, and SEM. The durability of the concrete against wet/dry cycles was investigated in terms of compressive strength, water absorption, open porosity, density, thermal conductivity, and electrical resistivity. The results showed that concrete mixes with CC and RHA up to 60% exhibited an increase of 33% in compressive strength, followed by minimal changes in water absorption. While a decrease in electrical resistivity was measured in all samples with RHA and CC, increasing the CC content to 50% resulted in improved resistance to chloride penetration. Increasing the CC content resulted in a more refined microstructure, with an overall decrease in porosity of up to 32% compared to the control series. While RHA alone did not contribute to significant improvements after wet/dry cycles, the combined substitution of RHA and CC at SCM replacement levels of 60% showed an overall improvement in hardened properties and durability. This investigation provides valuable insights into the long-term performance and strength of innovative low-carbon concrete.