civil engineering basics | vin civilworld

PCC concrete of Plain Cement Concrete (PCC) is without reinforcement steel. Plain cement concrete (PCC) is high in compression and very low in tension. Plain cement concrete is commonly used over the ground to keep footing reinforcement from coming into direct contact with the soil. The design mixes commonly used for Plain Cement Concrete (PCC) are 1:4:8, 1:3:5, 1:2:4, M7.5, M10 etc. PCC can also be used for grade slabs (floors) and concrete roads where the only load is compressive.

Concrete is a mixture of cement, sand, and aggregate (preferably broken stone) mixed with water in specific proportions. When poured into moulds or shuttered, the mixture consolidates over time to form a uniform mass known as concrete.

What is PCC Concrete or Plain cement Concrete in construction?

Concrete without reinforcement steel is called Plain Cement Concrete (PCC). Generally, design mixes commonly used for PCC are 1:4:8 , 1:3:5, 1:2:4, M7.5, M10 etc. Plain cement concrete is high in compression and very low in tension.

Properties of Plain Cement Concrete or PCC concrete

Plain cement Concrete (PCC) has compressive strengths ranging from 200 kg/cm2 to 500 kg/cm2. Likewise, tensile strength of PCC ranges from 50 kg/cm2 to 100 kg/cm2, and density ranges from 2200 kg to 2500 kg, depending on the grade of concrete and aggregates used.

Ingredients of Plain Cement Concrete or PCC Concrete

Basically, PCC is made from cement, coarse aggregate, and fine aggregate. Ordinary Portland cement is used as the binding material. Accordingly, as coarse aggregate, broken or crushed stone or brickbats must be used. However, fine aggregate must consist of coarse sand. Finally, these ingredients are combined in the appropriate proportions with potable water to make PCC.

Production of Plain Cement Concrete (PCC) in Construction

PCC can be manufactured in batching plants, mixer machines, or manually mixing. Generally, the thickness of PCC can range from 50 mm to 300 mm or more, depending on the design parameters.

Types of concrete in construction

The following are the main types of concrete used in construction

Plain cement concrete (PCC) — Plain cement concrete (**PCC )**

PLAIN CEMENT CONCRETE (PCC)
REINFORCED CEMENT CONCRETE (RCC)
PRESTRESSED CONCRETE
PRECAST CONCRETE
SELF COMPACTED CONCRETE

How to Decide On A Concrete Type

The type of concrete to be used on a particular work is decided based on following conditions.

Material Availability

Normally, the raw material (aggregate, sand, cement etc) availability decides the type of concrete to be used.

Strength Required

The concrete requires different strengths for different structures. However, the strength required for the particular structure decides the type of concrete to be used.

Construction methodology to be adopted

The construction technique to be adopted for a structure decides the type of concrete. Example Pre-stressed concrete etc.

Type of structure

Most of times the type of the structure decides the type of concrete to be used.

SELF COMPACTED CONCRETE (SCC) is preferred in structures where normal pouring is restricted due to rebar congestion or access restricted pouring area. SCC, when pumped from a single point, can fill every part of the structure.

Area of application

The type of concrete shall be decided by the area where it has to be used. In some structures, the reinforcement is so dense that concrete may not pass through it. Mostly, In those cases, specially designed concrete with small-size aggregates or Self compacted concrete (SCC) may be used.

Climate and pouring conditions

The areas where there is extreme weather conditions like heavy rain , extreme cold, extreme hot specially designed quick setting concrete will be used.

Placing of Plain Cement Concrete (PCC)

The following steps are followed while placing Plain Cement Concrete (PCC)

Level marking and dressing for PCC concrete

After completing the excavation, the bottom level of the PCC shall be marked on the ground using a level machine. The centre line from the survey pillars shall be transferred to the ground where PCC has to be done. The surface shall be dressed manually to remove the loose soil the surface level to receive PCC.

Surface Preperation and shuttering

The surface shall be neatly dressed and supports has to be placed around using wooden battens. Accordingly, the battens used have to be the same size as PCC preferably. The battens shall be properly supported using proper supports (scrap steel can be used). The dressed surface shall be sprinkled with water to avoid absorption of concrete water by the soil.

Placing and Finishing of PCC Concrete

Concrete must be poured from one end to the other. For levelling purposes, level pillars at 2 metre intervals must be provided. The concrete must be levelled and rammed in accordance with the level pillars and end supports. The slump for PCC should be approximately 75 mm. Concrete must be poured within 30-45 minutes.

Precautions while doing Plain Cement Concrete (PCC)

When excavating, take care to only excavate to the required levels. However, avoid over-excavation. Backfilling with loose earth is not recommended if the excavation depth exceeds the required depth. In that case, we can place the PCC at the required level by doing a plum concrete. Backfilling with soil and compaction with plate compactors/walk-behind rollers/or Vibro rollers, depending on the situation, is required.
Before beginning excavation, the PCC level must be transferred to different locations. Before fine dressing with lime powder, the centerline and PCC dimensions must be marked on the ground to avoid reworks.
The surface on which PCC is to be laid shall be sprinkled with water.
Anti Termite chemical or LDPE sheets may sometimes be used before doing PCC. A confirmation has to be taken before doing the PCC from the clients/customers.
The free-falling height of concrete shall be restricted to 1.5 meters due to segregation issues.

Foundation is the most significant part of any structure/building which transfers the total loads of the structure and its components to a competent surface on the ground. Foundations are broadly classified into two types. ie. Shallow and Deep Foundations.

Foundation is the last part of the structure which touches the ground. The area of contact with the ground is called the foundation bed.

Every structure is divided into:

a) Sub structure

b) Super structure

Components of a structure that are coming below the ground level are called substructure, and above ground level is called superstructure. Foundations are coming in the substructure category. Foundations are responsible for transferring loads of superstructure components to the ground.

HOW TO FIX TYPE AND SIZE OF FOUNDATIONS?

The selection of foundations depends on the bearing capacity of the soil and the purpose of the structure. Geotechnical engineering is a field of Civil Engineering, which analyses the physical and chemical properties of soil and furnish designers with the inputs on the soil properties and proposed types of foundations. The Safe bearing capacity of the soil determines the foundation type and dimensions.

SAFE BEARING CAPACITY OF SOIL

Bearing capacity is the capacity of soil to support a structure without settlement or failure. To keep the structure safe, the bearing capacity has to be calculated at different locations. The ultimate bearing capacity has to be divided by a factor to derive the safe bearing capacity of the soil. Safe bearing capacity is defined as the maximum load per unit area soil can withstand without settlement and failure. The safe bearing capacity is determined by conducting field tests or soil investigations.

QUALITIES OF A WELL DESIGNED FOUNDATION

A well-designed foundation is supposed to possess the following qualities.

a) Have to distribute the total load on the structure to a larger area.

b)Have to counter unequal settlement in case of any displacement.

c) Has to prevent the structure from lateral moments.

d) Foundations are responsible for the total stability of structures.

DIFFERENT TYPES OF FOUNDATIONS

Foundations are classified into

a) Shallow Foundation

b) Deep Foundation

SHALLOW FOUNDATION

Characteristics of shallow foundations

Shallow foundations are adopted when the load acting on a structure is reasonable and has a competent soil layer capable of negotiating the loads available at a shallow depth or shorter depth.

Shallow foundations are placed on the surface of the ground. The depth of a shallow foundation can range from 1 meter to 3.5 meters and sometimes more.

The width of the shallow foundation is greater than the depth. Shallow foundations are very easy to construct and do not require highly skilled manpower and professional supervision. These foundations can even be done with the help of medium-skilled workers. A shallow foundation is very economical when compared with a deep foundation. Shallow foundations are end bearing type foundations that transfer loads to the end of the foundation.

Shallow foundations are considered as the most preferred option when the safe bearing capacity of the soil is reasonable and the structural loads are within the permissible limits.

DEEP FOUNDATION

Characteristics of deep foundation

The width of the deep foundation is less than the depth. The depth can even go up to 60 meters or more depending on the design, loads, and availability of capable strata.

Deep foundations require technical expertise, sophisticated equipment, and highly skilled manpower for interpreting and executing works.

The deep foundations are costly due to their way of execution involving the infusion of quality materials, skilled labor, professional engineering support, and equipment

Deep foundations do not rely only on end bearing for transferring the loads. The skin friction developed between the foundation surface and the soil surrounding it may also be considered in the design stage.

The deep foundations can resist uplift pressure much more than shallow foundations and hence the chances of failure are less compared to shallow foundations.

SHALLOW FOUNDATION VS DEEP FOUNDATION