methodology

CHAPTER THREE: MATERIALS AND METHODS

3.1 Introduction
This chapter outlines the materials and methodologies employed in the project, with a focus on the procedures followed throughout. It details the sampling methods, data collection, and subsequent data processing and analysis. Stabilized rammed earth, a type of rammed earth construction, utilizes subsoils mixed with stabilizing agents to enhance the physical properties of the material. Soils used for cement-stabilized rammed earth typically have a higher content of sand and gravel and a lower content of fines. Organic matter in rammed earth construction should be avoided as it can lead to shrinkage, potential bio-deterioration, and increased vulnerability to insect attack. Organic material also hinders the effectiveness of stabilizers such as cement. To improve the mechanical strength and weathering resistance of the soil, it is beneficial to minimize the void ratio to increase particle contact.

3.2 Manufacturing Process of Cement
The primary ingredients used in cement manufacturing include:
a) Limestone
b) Calcium
c) Clay and shale
d) Silica/Alumina
e) Quarrying
f) Local resources (no market)

Limestone (CaCO₃) and clay are the two main raw materials used in the production of cement.

3.2.1 Portland Cement Clinker
a) Clays contain varying amounts of SiO₂ and Al₂O₃.
b) The manufacturing process of Portland cement involves grinding raw materials, mixing them in appropriate proportions, and burning the mixture in a kiln at temperatures between 1400-1500⁰C. This process partially fuses the material into balls known as clinker, which is then ground with a small amount of gypsum rock.
c) The raw material mixture is burned in a rotary kiln.

3.2.2 Type of Cement and Its Physical Properties
The cement used in this project was Hima cement (32.5N), with its physical and chemical properties verified by the manufacturer through a testing certificate.

1. Setting Time
   The setting time of cement paste is influenced by factors such as cement fineness, water-cement ratio, chemical content (especially gypsum content), and admixtures. Setting tests determine how the cement paste sets, with both initial and final setting times being crucial for construction purposes. Additional setting times include:
   • Initial Set: Occurs when the paste begins to stiffen.
   • Final Set: Occurs when the cement has hardened enough to sustain a load, primarily influenced by C3A and C3S, leading to a temperature increase in the cement paste.
   • False Set: No heat is generated, and the concrete can be remixed without adding water. This occurs due to the conversion of unhydrated/semi-hydrated gypsum to hydrous gypsum (CaSO₄·2H₂O).
   • Flash Set: Caused by the absence of gypsum and specifically used for underwater repairs.

   Setting time tests are conducted using the Vicat apparatus with a 1mm diameter needle. The times are arbitrary points used to characterize cement and lack fundamental chemical significance. Both the Vicat needle and Gillmore needle tests define initial and final setting times based on needle penetration into the cement paste, with the Vicat test typically producing shorter times as per ASTM C 150.

2. Soundness
   Soundness in Portland cement refers to the ability of hardened cement paste to retain its volume after setting without delayed expansion, often caused by excessive free lime (CaO) or magnesia (MgO). Specifications limit magnesia content and expansion to prevent volume changes after setting. The presence of excessive free CaO or MgO can lead to delayed hydration and expansion of the hardened paste. Soundness is defined as the volume stability of the cement paste, with the ACI-prescribed soundness test conducted using the Le Chatelier apparatus.
3. Fineness
   The fineness, or particle size, of Portland cement affects the hydration rate and strength development rate. Smaller particle size increases the surface area-to-volume ratio, providing more area for water-cement interaction. The effects of finer particles are noticeable in the first seven days, with coarser particles potentially not fully hydrating, leading to lower strength and durability. High fineness is necessary for rapid strength development, with the Blaine air-permeability method being the most common method for determining cement particle fineness.
4. Strength
   Cement paste strength is measured in terms of compressive, tensile, and flexural strength. These can be affected by the water-cement ratio, cement-fine aggregate ratio, type and grading of fine aggregate, curing conditions, specimen size and shape, loading conditions, and age.

3.2.3 Duration of Testing
Testing durations typically include: a) 1 day (for high early strength cement)
b) 3 days, 7 days, 28 days, and 90 days (to monitor strength progress)
c) 28 days strength is commonly used as a control basis in most codes.

When considering cement paste strength tests, it’s important to note:

• Cement mortar strength does not directly relate to concrete strength; tests are conducted on cement mortars (cement + water + sand) rather than cement pastes.
• Soil used in rammed earth structures was free from organic materials and other non-soil substances, such as rubbish and deleterious materials.

Rammed earth soils were composed of approximately 50% to 70% fine gravel and sand, 15% to 30% silt, and 5% to 15% clay. Particle size distribution was used to obtain these proportions in accordance with BS standards. Soil mixtures were tested using the “roll” method, where the break-off length should be between 80mm and 120mm. Deleterious materials, such as soils containing salts like sulfates, which interfere with binder setting, were avoided. Soil samples were excavated from the site, tested for suitability, and evaluated for the need for additional additives. Field tests were conducted on samples taken from a depth of 1 meter to ensure surface organic materials were excluded.

3.3 The Jar Test: Particle Size Test
To determine the proportions of different particle sizes in the soil, a jar test was conducted. This preliminary assessment involved filling two-thirds of a bottle with soil from the site, adding water to fill the bottle, shaking it to suspend the soil particles, and allowing it to settle. As the water cleared, distinct soil layers formed, with sand settling at the bottom due to its heavier particles, followed by layers of silt and clay.

The material was excavated to a depth of 7 meters below the ground surface within the structural vicinity and piled into heaps to prevent contamination with topsoil and impurities. The heap was kept compact to avoid external influences and to maintain the Optimum Moisture Content (OMC). The material was sieved to aerate the soil and remove lumps, stones, and pebbles.

Soil, sand, and stabilizer components were accurately measured and mixed in the container using hand tools such as hoes and spades. The mixing process followed this order: a) Pour in the soil and stabilizer (cement).
b) Mix the material dry 2 to 3 times.
c) Add water and mix it wet 2 to 3 times.

The material was mixed to its OMC to achieve Maximum Dry Density (MDD) and maximum strength. Laboratory tests, including compressive tests for the rammed earth structure, were conducted and are included in the appendices. The mixed material was transported to the building area using wheelbarrows and poured into the formwork.

Formwork was set up and checked with a plumb line to ensure vertical alignment. The material was poured into the formwork in layers of 120mm thickness. Before ramming, a layer gauge (6mm diameter MS void) was used to check the thickness of the loose soil. The soil was then rammed, starting from the sides of the panels and moving to the center until a sharp sound indicated proper compaction. After ramming, the formwork was left for 2-3 hours before being dismantled and the process repeated. Formwork was never left in place overnight.

The rammed earth structure was constructed with a wall thickness of 450mm on the ground floor and 350mm on the upper floor, designed to provide thermal mass, especially in tropical regions. False walls were also constructed to accommodate high-end home entertainment systems, project screens, and conceal speakers.

A mix ratio of 1:7 (1 bag of cement to 7 wheelbarrows of excavated soil) was used. Columns were sized at 400x400mm, and beams at 400x150mm.

Traditional burned clay bricks construction involves building structures by laying individual masonry units with bricks, using cement mortar to bind them together. This method provides aesthetically pleasing walls and floors at economical prices.

Using a 2MPa compressive strength criterion as the measure of stabilization success, soil properties were related to the proportion of samples exceeding the criterion. Linear shrinkage (LS) and plasticity index (PI) were found to be the best indicators of soil suitability, with textural variables serving as secondary indicators. “Favorable” soils, with stabilization success rates of ≥80%, include those with:

1. LS<6.0% and PI<15%
2. LS 6.0–11.0%, PI 15–30%, and sand content <64%.

These soils were stabilized with treatments averaging 4.2% cement and 1.8% lime, with individual treatments ranging from 4–8% total cement and/or lime. “Unfavorable” soils, with stabilization success rates of <60%, include those with LS 6.0–11.0%, PI