Lime vs cement

When we discuss the sustainability of materials, most folks only ponder the eco-friendliness during the performance, overlooking the material’s life cycle. Where it originates and where it ends. The social and economic sustainability aspects are often overlooked entirely.

Ecological sustainability

Comparing lime with cement is a great way to showcase the complete sustainability picture. Limestone is plentiful in nature. Both lime and cement require heat, with lime needing around 900°C and cement around 1450°C. While 900°C can be attained with renewable sources like charcoal, coal is predominantly used. When limestone is burned, carbon dioxide is emitted, transforming it into quicklime. After hydration, quicklime becomes slaked lime, releasing heat, often wasted. Slaked lime mortar is used for various purposes. As it sets, it absorbs carbon dioxide, reverting to limestone, the original material.

In contrast, cement, a blend of lime, clay, and additives, deviates entirely from natural origins, resulting in waste alien to nature.

Understanding this cradle-to-grave cycle is crucial for sustainability. Everything eventually becomes waste. Our chemical industry converts many daily products into new materials, challenging nature’s waste management. Sustainable thinking involves considering waste management—ideally, minimizing waste or repurposing it into useful materials.

Economical sustainability

What’s often conveniently overlooked in discussions about sustainability is the aspect of economic sustainability. While the commercial sector may readily highlight ecological considerations, there’s often a reluctance to delve into the economic sustainability of materials and constructions.

A pivotal but often disregarded aspect is the lifespan of cement-based structures. Typically, these constructions endure for 50 to 70 years.

One cause is the reaction called sulfurization. Sulfate ions, often from pollutants or natural sources, react with calcium hydroxide in concrete to form gypsum. This reaction can also lead to the formation of ettringite, especially if the reaction occurs at later stages after the concrete has been set. Both gypsum and ettringite take up more volume than the original materials in the cement. This expansion creates internal stress. The internal stress from this expansion can lead to cracking, spalling, and overall weakening of the concrete structure.

The lifespan of cement-based structures can be significantly reduced due to sulfurization. The durability is compromised as the material becomes more porous and less structurally sound. In severe cases, structural integrity can be threatened, requiring extensive repairs or even replacement of the affected parts.

Other causes reducing the lifespan of cement-based constructions are:

Chloride Attack: Chlorides, especially from marine environments or de-icing salts, can penetrate concrete and corrode the steel reinforcement inside, leading to structural weakness.

Carbonation: Carbon dioxide from the air reacts with the calcium hydroxide in concrete, lowering the pH and reducing the passivation layer on reinforcing steel, which can lead to corrosion.

Freeze-Thaw Cycles: In colder climates, water that has penetrated concrete can freeze and expand, causing cracking and spalling.

Abrasion: Continuous wear and tear from vehicles, machinery, or even foot traffic can erode the surface of concrete, exposing and weakening the underlying structure.

Impact and Overload: Impacts or excessive load can cause cracks and structural compromise.

Temperature Fluctuations: Repeated expansion and contraction due to significant temperature changes can cause thermal cracking.

Continuous exposure to moisture not only facilitates chemical attacks but also leads to physical damage like swelling and shrinkage of the concrete matrix.

Ultraviolet (UV) Radiation: UV light can degrade certain concrete additives and surface treatments, though concrete itself is generally UV stable.

Certain bacteria can produce acids that degrade concrete or corrode metallic components within concrete structures.

On the other hand Iime-based constructions often have a longer lifespan than cement-based constructions for several reasons, each linked to the inherent properties of lime and how it interacts with its environment over time.

Lime mortar is more flexible compared to cement mortar. This flexibility allows lime-based structures to absorb and accommodate movements and settlements without cracking as much as cement-based structures. 

Lime has self-healing properties. When small cracks do form, the continued carbonation of the free lime within the mortar can lead to the deposition of lime in these cracks, effectively “healing” them. 

Lime is highly permeable in water vapor, allowing buildings to “breathe.” This means moisture can easily escape, preventing the build-up of dampness and the related deterioration issues seen in less permeable cement-based structures.

Lime’s ability to manage moisture reduces the risk of trapped moisture, which can cause long-term damage such as frost damage in colder climates or salt damage in coastal areas.

Lime-based mortars are particularly durable over time, especially in environments that undergo cycles of wetting and drying.

They are less prone to the detrimental effects of sulfate attack, a common problem for cement in environments with high sulfate content.

For restoration projects, lime mortar is often preferred because it is compatible with the materials used in historic buildings. Using cement in such contexts can lead to faster deterioration of the original materials due to the harder and less flexible nature of cement.

Lime-based constructions are more suited to withstand environmental conditions that can cause deterioration in cement-based constructions, like acidic environments where cement can break down more quickly.

Lime mortars and plasters have been used for thousands of years, and many ancient structures that utilized lime are still standing today, which is a testament to its durability. Cement, while stronger in the short term, doesn’t always have the same longevity, especially under conditions that favor the strengths of lime, such as flexibility and breathability.

While cement might offer superior initial strength, lime-based constructions provide long-term durability, especially under fluctuating environmental conditions and in heritage conservation, contributing to their often longer lifespan.

Economic sustainability hinges significantly on the lifespan of products and constructions. However, the commercial world often shies away from longevity, as it challenges the paradigm of planned obsolescence. In our consumer-driven society, where economic growth is synonymous with continuous consumption, longer-lasting products pose a conundrum for industries reliant on frequent
purchases to sustain financial growth. This perpetual cycle of consumption not only depletes finite natural resources but also contributes to the mounting problem of waste accumulation.

In architectural design, embracing economic sustainability entails prioritizing timeless designs that stand the test of time. While modern contemporary buildings may captivate with their avant-garde esthetics, they often fall out of favor within a few decades, succumbing to changing trends and evolving tastes.

Architects play a pivotal role in fostering economic sustainability through their design choices. By eschewing fleeting trends in favor of timeless design principles, architects can create spaces that not only withstand the ravages of time but also evoke a sense of timelessness and permanence. Incorporating elements of traditional architecture, such as vernacular building techniques and
locally sourced materials not only enhances the esthetic appeal of the structure but also promotes environmental sustainability by reducing the carbon footprint associated with construction. Furthermore, designing with longevity in mind extends beyond esthetics to encompass functionality and adaptability. By prioritizing flexible floor plans and durable materials, architects can future-proof buildings, ensuring that they remain functional and relevant for generations to come.

In essence, embracing economic sustainability in architectural design involves a shift towards timeless designs that endure beyond passing trends. By prioritizing enduring esthetics, cultural relevance, and environmental responsibility, architects can create spaces that enrich lives, foster a sense of belonging, and contribute to a more sustainable built environment for future generations.

Not only in construction but in almost every section of the manufacturing industry, we can see the trend of reducing the lifespan of products in order to achieve more financial gain.

For example, in the realm of furniture, the choice between a mass-produced chair crafted from fibreboards and synthetic upholstery, prone to disintegration after a few years, and a handcrafted wooden chair from a skilled carpenter presents a stark juxtaposition in terms of longevity and sustainability. Opting for the former may offer immediate convenience and affordability, but it comes at the cost of durability and environmental impact. These chairs, often constructed with low-quality materials and adhesives, are destined for a short lifespan before succumbing to wear and tear, ultimately ending up as waste in landfills.

Conversely, investing in a meticulously crafted wooden chair from a skilled artisan promises longevity and sustainability. Crafted without the use of harmful glues and varnishes, these chairs not only offer comfort and esthetic appeal but also boast a lifespan that extends across generations. The inherent durability of wood, coupled with the craftsmanship of a skilled carpenter, ensures that these chairs withstand the test of time, becoming cherished heirlooms rather than disposable commodities.

Moreover, choosing wooden furniture promotes environmental sustainability by supporting responsible forestry practices and reducing reliance on synthetic materials derived from finite resources. By opting for quality over quantity and investing in timeless pieces crafted with care and consideration, we not only enhance the longevity of our furniture but also contribute to a more sustainable future for generations to come.

Social sustainability.

Consider the cement industry in India, which is controlled by a few families. A bag of cement sells for about 400 rupees, while the cost of production, transport, and retail is roughly 200 rupees. Given the constant demand for cement across the country, these families enjoy a substantial income. Now, compare this with the thousands of families who could sustain themselves by operating local lime kilns. 

This contrast highlights an essential aspect of social sustainability. In our globalized world, many products we use are sourced from various international locations. Often, we lack clear information about the production processes, the environmental impact of resource extraction, and whether workers are compensated fairly and work under humane conditions, or if exploitation, including child labor, is involved. It’s crucial not to overlook the social dimension of sustainability. We should strive to purchase locally-produced goods as much as possible, where the production chain is transparent. For example, buying from local artisans and
farmers not only support the local economy but also reduce our carbon footprint and ensure fair labor practices. By making informed choices about where our products come from, we contribute to a more socially sustainable world.

In conclusion, the lime versus cement debate exemplifies the broader challenges and opportunities within sustainable practices across industries. While cement offers strength and is ubiquitous in modern infrastructure, its production often involves significant environmental impact and centralizes economic power. Lime, though less commonly used, highlights the potential for sustainable practices to enhance local economies, reduce energy consumption, and support environmentally friendly methods. This comparison sheds light on the necessity of evaluating long-term environmental and social implications in material choices, advocating for more thoughtful and sustainable decision-making in various sectors, not just construction. Such an approach encourages us to prioritize
materials and processes that are not only effective but also ethical and sustainable, ensuring a healthier planet and equitable communities.