Chapter 15
Reengineering Ancient Materials for Durable, Low-carbon Structures
Anwar Khitab*, Hussnain Talib, Faheem Aziz Ahmed, and Ahmed Raza
Department of Civil Engineering, Mirpur University of Science and Technology (MUST) Mirpur-10250 (AJ&K) Pakistan
Abstract
Ancient structures exemplify sustainable construction by utilising locally available and recycled materials such as lime, sand, brick dust, charcoal, legume flour, and small aggregates in their binders. Beyond lime and sand, these components are primarily waste products, brick powder acts as a pozzolan, charcoal enhances workability, and legume flour improves shrinkage resistance, cohesion, and flexural strength. Such eco-friendly mixtures have ensured durability for centuries, outlasting modern cementitious systems. This study focuses on Ramkot Fort, a 900-year-old structure built in 1186 by Sultan Ghayas-Ud-Din, which remains intact despite severe environmental stresses including earthquakes, weathering, and thermal shocks induced by climate change. Detailed analysis of the original mortar revealed a lightweight, breathable composition with low strength but high resilience. A compatible repair mortar was formulated using hydrated lime, local clay, sand, crushed brick, and optimised with polypropylene (PP) fibres to mitigate shrinkage cracks observed under high ambient temperatures (~45 °C). The new mix achieved enhanced mechanical properties (compressive strength of 1.27 MPa, flexural strength of 1.32 MPa, bond strength of 3.51 MPa) while maintaining breathability and thermal stability. This research proposes a prototype mortar, merging ancient practices with modern improvements, offering a climate-resilient, sustainable, and durable solution for heritage conservation and future eco-friendly construction.
Keywords: Traditional materials, Modern techniques, Sustainable mortars, Heritage conservation, Climate resilience.
Introduction
The survival of ancient structures for centuries stands as a testament to the wisdom of traditional construction practices. These structures, built without modern cement, utilised locally available materials such as lime, sand, crushed bricks, charcoal, and organic additives like legume flour, black gram, among others. Such materials, often derived from natural or waste resources, provided durability, breathability, and compatibility with the surrounding environment. In contrast, modern cement-based systems, while offering rapid strength gain, have shown limitations in longevity, especially under harsh climatic conditions. With growing concerns about the environmental impact of cement production and the need to conserve heritage sites, there is increasing interest in revisiting ancient material formulations. This study discusses the integration of traditional materials with modern reinforcement techniques to develop sustainable, durable, and climate-resilient repair mortars for the conservation of historic masonry structures as well as for future low-carbon construction.
To establish a foundation for this approach, a review of previous research on ancient mortar compositions, natural admixtures, and modern strengthening interventions is necessary. The following section summarises key findings from the literature, highlighting successful examples and research gaps relevant to heritage mortar repair.
Fort et al. (2023) studied the ancient Roman villas of Żejtun in Malta1. The ancient mortar was prepared using local materials: hydrated lime, reactive aggregates (ceramic and rock fragments), and additive (ceramic powder). The combination of aerial lime with reactive aggregates such as volcanic ash (pozzolana) resulting in a material with hydraulic properties, is considered a remarkable technological achievement of the ancient Romans. This centuries-old approach holds significant relevance for a sustainable future, as it demonstrates how durable construction materials can be developed using low-energy lime binders and locally sourced industrial by-products or natural pozzolans. By minimising dependence on energy-intensive Portland cement and encouraging the use of locally available reactive materials, this technique offers a pathway to reduce carbon emissions, conserve natural resources, and promote environmentally responsible construction practices. Manoharan and Umarani (2022) analysed the ancient temples of Tamil Nadu in India2. The results revealed the presence of calcite, silica, and amides. While the first two indicate hydrated lime and sand, the last one indicates the presence of organic proteins. Regional plants rich in carbohydrates, proteins, and fats were traditionally incorporated into lime mortar mixtures, serving as multifunctional additives for enhancing workability, cohesion, and long-term durability of the mortar matrix3. Pradeep et al. (2022) have indicated that the addition of fermented plants enhanced the carbonation of limes and strength4. Tsoupra et al. (2022) analysed lime mortars from heritage structures in Kathmandu Nepal5. FTIR and chemical tests confirmed the use of organic additives, including black lentil (black gram). The presence of black lentil suggests its historical use to enhance mortar properties. Although exact fermentation recipes are not provided, the study confirms the addition of lentil-derived organics, likely in paste or water form.
The present study focuses on the development of mortar specimens composed of hydrated lime, sand, brick particles and powder, and polypropylene (PP) fibres. The specimens were evaluated for key physical and mechanical properties. This research aims to formulate a contemporary lime-based mortar suitable for the rehabilitation of architectural heritage sites, while also promoting sustainable construction practices inspired by traditional building techniques.
Materials and Methods
Original mortar samples extracted from Ramkot Fort were subjected to general characterisation using modern ASTM and RILEM protocols. Physical properties (density and porosity), chemical composition, and particle size distribution were determined to identify the binder and aggregate fractions. A compact methods table listing test standards, specimen dimensions, curing regime, age at test, and loading rate is given in the form of Table 1. Based on these analyses, the constituent materials and their unit proportions were established. The mortar specimens were accordingly prepared and compared with the modern-day cement sand mortar. For this purpose, a reference cement mortar representative of contemporary masonry practice was prepared with a mix ratio of 1:4 (cement to sand by volume) and a water-to-cement ratio of 0.6. The specimens were prepared and water-cured in accordance with ASTM C109 method6. The characteristics were determined after a curing period of 28 days.
Table 1: Summary of experimental methods and test parameters.
|
Property |
|
Standard |
|
Specimen dimensions |
|
Curing regime |
|
Age (days) |
|
Loading rate/condition |
|
Density and porosity (lime/cement) |
ASTM C642–217 |
50 × 50 × 50 mm cubes |
Moist-cured 27 ± 2°C/ Oven-dried at 105°C, then water-immersed |
28 |
— |
|||||
|
Chemical composition (XRD / XRF) |
|
|
Powdered samples (<75 µm) |
|
— |
|
— |
|
— |
|
|
Particle size distribution |
|
ASTM D6913-04(2009)e-1-1710 |
|
— |
|
Oven-dried before sieving |
|
— |
|
Mechanical shaker (10 min) |
|
Reference cement mortar preparation |
|
ASTM C109–2011 |
|
1:4, cubes 50 mm. |
|
Water-cured at 27 ± 2 °C |
|
28 |
|
— |
|
Bond strength test |
|
RILEM LUM B1 (Modified)12 |
|
Brick–mortar–brick prisms |
|
Water-cured at 27 ± 2 °C |
|
28 |
|
0.05 MPa/s |
Figure 1: Ingredients, composition, and casting of prototypes.
Results and Discussion
Prototype specimens as well as contemporary cement sand mortar samples were tested in terms of flow, density, appearance, and mechanical strength and the results are summarized in Figure 2 and Figure 3.
The lime mortar, composed of lime, sand, clay, and brick particles, demonstrated a lower density (1.8 vs. 2.1 g/cm³) and higher flow (150 vs. 100 mm) than cement mortar at equal water content. Despite its lightweight nature, the lime mortar attained a bond strength (3.51 MPa) comparable to cement mortar (3.98 MPa). It should also be noted that lime mortars gain strength slowly compared to their cement counterpart. The higher flow can be attributed to lime, the fine brick, and clay particles, which enhance lubrication within the mix, while the reduced density reflects its porous and breathable structure, beneficial for moisture regulation in historic masonry. The incorporation of PP fibres further improved crack resistance under elevated temperatures (~45 °C), ensuring better dimensional stability in hot climates. Beyond thermal and mechanical performance, the brick particles impart a distinctive pink colour, ensuring better visual integration with heritage structures. The statistical summary of the materials is presented in Table 2. All quantitative tests were conducted in triplicate (n = 3), and mean values along with standard deviations are reported. Given the limited number of replicates, the results should be interpreted as indicative trends rather than statistically validated population parameters.
|
Figure 2: Comparison between lime-brick powder with modern day cement mortar in terms of flow, aesthetics, sustainability, weight, and strength. |
|
Figure 3: Comparison between lime-brick powder with modern day cement mortar in terms of crack resistance at high ambient temperature (~45℃). |
|
Table 2: Summary of physical and mechanical properties of the investigated mortars (mean ± standard deviation, n = 3). |
|||||||||
|
Specimen |
|
Density (g/cm³) |
|
Porosity (%) |
|
Bond strength (MPa) |
|
Flexural strength (MPa) |
|
|
Cement mortar |
|
2.03 ± 0.03 |
|
11.80 ± 0.36 |
|
3.98 ± 0.06 |
|
2.69 ± 0.07 |
|
|
Heritage-replicated mortar |
|
1.83 ± 0.02 |
|
29.76 ± 0.86 |
|
3.51 ± 0.04 |
|
1.29 ± 0.06 |
|
In this study, the lime–PP mortar performed comparably to the reference cement mortar while offering added benefits of breathability, ductility, and improved compatibility with historic masonry. The use of local clays and recycled brick waste enhance sustainability, whilst the incorporation of PP fibres may prove beneficial in earthquake-prone regions owing to their energy-absorbing capacity. These outcomes, together with previous findings in the literature highlighting the advantages of lime-based mortars over cement mortars in heritage contexts, suggest that the proposed lime–PP system represents a climate-resilient, sustainable, and heritage-compatible alternative for conservation and environmentally friendly construction.
Although a full life‐cycle analysis is beyond the current scope, published emission factors indicate that producing Portland cement emits about 0.82–0.90 kg CO₂ per kg of cement13, whereas producing quicklime via calcination carries emissions of about 0.8 kg CO₂ per kg (calcination only)14. Considering that lime mortars often require less processing temperature (around 900 °C compared to ~1450 °C for Portland cement), use fewer high-emission energy inputs, and allow for considerable CO₂ re-absorption during carbonation, the net embodied carbon of lime‐based mortars can be substantially lower than that of cement mortars.
Conclusions
The lime mortar formulated with sand, clay, brick particles, and PP fibres proved to be lightweight, workable, and mechanically comparable to cement mortar, whilst offering superior breathability and reduced cracking under thermal stress. Its aesthetic compatibility, cost-effectiveness, and reliance on locally available recycled materials further add to its value. Taken together, these characteristics, along with indications from the literature, suggest that the lime–PP system is a climate-resilient and heritage-compatible option for conservation and environmentally friendly construction.
The findings of this study establish a laboratory-scale foundation for developing durable and low-carbon lime-based mortars. However, their scalability and field performance require further validation. Future work should focus on pilot-scale production and field trials under varying climatic and substrate conditions to assess long-term durability, mechanical stability, and compatibility with existing heritage materials. Limitations of the present study include the restricted number of mix compositions and controlled curing conditions, which may not fully replicate on-site variability. Extending this work toward standardised mix design protocols and regional raw material optimisation will enable broader practical implementation in sustainable and heritage construction.
References
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ASTM C1365-18. “Test Method for Determination of the Proportion of Phases in Portland Cement and Portland-Cement Clinker Using X-Ray Powder Diffraction Analysis.” West Conshohocken, PA, 19428-2959 USA: ASTM International, March 1, 2018. https://doi.org/10.1520/C1365-18.
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