Cement

Introduction

Cement is a fine powder made from a mixture of limestone, clay, and other minerals that are calcined at high temperatures. When mixed with water, it forms a paste that hardens and binds together aggregates, creating a solid and durable construction material.

Uses/benefits:

Cement is extensively used in tunneling and underground structures for the following purposes:

Concrete Construction: Cement is a primary ingredient in concrete, which is used for the construction of tunnel linings, shafts, floors, walls, and other structural elements. It provides strength, stability, and durability to the concrete structures.
Grouting: Cement-based grouts are used for various applications in tunneling, such as ground stabilization, water control, and filling voids or fractures. Cement grouting improves the stability of the surrounding ground and enhances the performance of the tunnel or underground structure.
Shotcrete: Cement-based shotcrete, also known as sprayed concrete, is used for the rapid construction of tunnel linings. It is applied pneumatically onto the excavated surface, providing immediate support and sealing against water ingress.
Mortar: Cement is an essential component of mortar, which is used for masonry work in tunnel construction. Mortar provides adhesion and cohesion between bricks, blocks, or stones, forming a strong and durable bond.
Soil Stabilization: Cement is used for soil stabilization in tunneling projects, particularly in weak or unstable ground conditions. Cement stabilization improves the engineering properties of the soil, such as strength, compressibility, and durability, making it suitable for tunneling.

Specifications:

Specifications for cement in tunneling and underground structures may vary depending on the specific project requirements and applicable standards. Some common specifications include:

Cement Type: Different types of cement, such as Portland cement, blended cement, or specialty cement, may be specified based on factors like strength, setting time, sulfate resistance, and environmental considerations.
Compressive Strength (IS 4031-6 :1988): The compressive strength of cement is an important specification, indicating its ability to withstand loads and provide structural stability. The required strength depends on the specific application and design requirements.
Setting Time (IS:4031(Part 5):1988): The setting time of cement refers to the time it takes for the cement paste to harden. It is important to consider the initial setting time and final setting time to ensure proper workability and curing of the cement.
Consistency and Workability (IS 4031 (Part 4): 1988): The consistency and workability of cement paste or mortar are specified to ensure proper mixing, application, and placement of the cement-based materials.
Chemical Composition: The chemical composition of cement, including the presence of minerals, additives, or admixtures, can be specified to achieve desired properties such as improved workability, reduced shrinkage, or enhanced durability.

Types:

Different types of cement are available for tunneling and underground structures, including:

Ordinary Portland Cement (OPC): OPC is the most common type of cement used in construction. It is suitable for a wide range of applications and provides good strength and durability. OPC 33 grade, 43 grade and 53 grade Shall be used in according to the IS:269, IS:8112-1989 and IS: 12269-1987, respectively.
Blended Cement: Blended cement is a mixture of OPC and supplementary cementitious materials such as fly ash, slag, or silica fume. Blended cement offers enhanced properties, including improved workability, reduced heat of hydration, and increased resistance to sulphate attack.
Rapid Hardening Cement: Rapid hardening cement (IS 8041:1990) is designed to achieve high early strength development, making it suitable for projects with quick turnaround times or where early strength is crucial. RHC is known as type-III cement according to ASTM C 150.
Low Heat Cement: Low heat cement (IS 12600 :1989) generates less heat during hydration, making it suitable for massive concrete structures to prevent thermal cracking. LHC is known as type-IV cement according to ASTM C 150.
Sulphate-Resistant Cement: Sulphate-resistant cement (IS:12330) is used in environments where the ground or water contains high levels of sulphate ions, which can cause deterioration of concrete over time. SRC is known as type-II & V cement according to ASTM C 150.

It is important to follow relevant industry standards, local regulations, and consult with engineers or construction professionals to determine the appropriate cement type and specifications for tunneling and underground structure projects.