Dr Alice Nabatanzi: The writer, a PhD holder in phytochemistry and neutraceuticals, is a lecturer in the Department of Plant Sciences, Microbiology and Biotechnology in the College of Natural Sciences, Makerere University
Due to the highly competitive market for building materials where margins are constantly under pressure, operational excellence combined with greater efficiency is key to achieving profitability. Thus, the strong move by 8M Construction Digest to investigate and explore the locally available construction materials for affordable housing and sustainability.
Cactus (cacti/cactuses – plural) is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. Cacti are prickly and pleasing. Extremely ungainly, they flourish in arid conditions where no plant can survive. Succulent inside, their thick coats and nettles ensure predators cannot get to the sap inside. Cacti are very much treasured for their wood and gum/sap.
Various types of cactus plants produce wood, though unlike common wood producers like pine, maple and oak trees, cactus wood is hidden behind the plants’ layers. Cacti contain layers of spines that provide protection from animals and, in some cases, the sun. These spines attach to the thick green or grey skin of the cactus, which helps retain moisture by preventing transpiration, or evaporation. Underneath this skin, large species of the cactus possess thick wood bodies much like those of small trees.
Cacti exhibit specific tendencies through their wood. Many cactus species exhibit polymorphic wood growth. This means the plants grow different types of wood at different stages in their development. All large species of cacti possess wood with especially high fibre content, which makes the wood extremely strong. Cactus plants evolve such that successive generations of plants store larger amounts of water in their wood than did their parents. Storing water in the wood with the use of specialized vessels increases the overall storage capacity of a plant and allows it to withstand longer periods of drought than it could without storing water in such a way.
There is a direct correlation between the types of fibre and the size of water conduction and storage vessels found in cactus wood and the growth habit of cactus species. The larger the cacti, the longer and wider the water vessels and fibres. This means that the largest cactus plants possess the strongest wood and the capacity to store the most amount of water, an obvious evolutionary trait that helps large cacti survive in harsh conditions.
In ancient times, locally available natural polymers were used to improve the durability of lime-based mortars and concretes. Today, cactus gum can be used as a natural polymer. It increases the plasticity of the mortar and improves water absorption and freeze-salt resistance, thereby increasing strength and durability. Furthermore, when concrete is painted with cactus gum it improves water resistance.
There are a great many raw materials in Uganda. The cactus is one of them, waiting for applied research in construction among the engineering fraternity. Over to you.