Concrete Mix Design for different grades of concrete

Concrete Mix Design is the process for choosing appropriate elements of concrete and finding out their relevant ratios with the purpose of developing concrete with specific minimum strength and stability as inexpensively as possible.

Purpose of mix design

To make sure the most favorable ratios of the ingredients of concrete to satisfy the need of the structure that should be built up. Mix design is used for the following purposes :-

To attain the designed/required adaptability in the plastic phase.

To attain required minimum stability in the hardened phase.

To attain the required stability in the specified environment conditions.

To form concrete as inexpensively as possible.

Designing of concrete mix is dependent on the following factors :-

1. Cost
2. Specification
3. Workability
4. Strength and Durability

Given below, the details of concrete mix design for different concrete grades like M20, M25, M30 and higher grades :-

www.onlinecivilforum.com



~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Use and benefits of self compacting concrete

Self-consolidating concrete alias self-compacting concrete (SCC) is a concrete mixture that can flow into very complex forms with various reinforcing bars (rebar congestion) and leaves no voids.

It can be arranged with its own weight devoid of any mechanical vibration. SCC retains all the conventional mechanical and durability characteristics of concrete.

With extremely fluid nature of SCC, it becomes possible to arrange it in complicated conditions and in sections with congested reinforcement. It can also reduce hearing-related damages on the worksite due to vibration of concrete. In SSC, the required time is curtailed significantly for arranging bigger sections.

In some cases, the superplasticizers and viscosity modifier are provided to the mix to minimize bleeding and segregation.

A well designed SCC mix never segregates because it contains extreme deformability and outstanding stability characteristics.

Self-Compacting Concrete Properties: Self-compacting concrete has good resistance capacity against segregation as it applies mineral fillers or fines as well as special admixtures. Self-consolidating concrete is essential to flow and fill special forms under its own weight. It is flown adequately to travel over extremely reinforced areas, and should have capability to circumvent segregation of aggregate.

Self-compacting concrete contains an equivalent water cement or cement binder ratio that provides normally a slightly higher strength with regards to conventional vibrated concrete and because of non-existence of vibration, a better interface among the aggregate and hardened paste is created.

The concrete mix of SCC should be arranged at a comparatively greater velocity as compared to regular concrete. Self-compacting concrete is placed from heights longer than 5 meters exclusive of aggregate segregation. It is also useful for areas having normal and congested reinforcement, with aggregates as large as 2 inches.

Self-Compacting Concrete Uses - Self-compacting concrete is mostly utilized in bridges and even on pre-cast sections. This type of concrete is suitable for the following:

• Drilled shafts
• Columns
• Earth retaining systems
• Areas with high concentration of rebar and pipes/conduits

To know about the benefits of self consolidating concrete, go through the following link thebalance.com



~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Slipformed Concrete and its advantages

Slip forming alias continuous poured, continuously formed, or slipform construction stand for a construction process in which concrete is poured into a constantly moving form. Slip forming is employed for high structures (like bridges, towers, buildings, and dams), as well as horizontal structures, like roadways.

Under the slipforming method, the formwork is shifted ceaselessly in sync with the concreting method in a 24-hour operation. The formwork along with the working platform and the hanging scaffold lifted inwardly or on both sides, is attached to the jacking rods in the center of the wall. The lifting jack that runs with hydraulic oil increases the formwork by 15 to 30 cm per hour on the basis of the temperature. The jacking rods are set in pipe sleeves at the top and are supported with the concrete that is already solidified. The rods and sleeves are also expanded endlessly. Mainly, the specialist contractors perform these work completely.

Slipforming is a rapid and well-organized method. The method is specifically applicable for simple, stable ground plans and following high structures:

 High bay warehouses, silos§
 Tower and chimney structures§
 Shaft structures§

As the height of the formwork is normally around 1.20 m and per hour production rate is 20 to 30 cm, the concrete beneath is 4–6 hours old and should be sufficiently rigid to carry its own weight (green strength). Though, it should not have arranged adequately for some of it to fix to the rising formwork (“plucking”). The main purpose of slipforming devoid of any issue is to start concreting all areas at the same level all together, and then perform the setting of these layers all at once. So, the temperature plays an important role together with the need for the constantly optimum w/c ratio.

Composition:
 Aggregate 0–32 mm, or 0–16 mm for close reinforcement§
 Despite the fact that slipformed concrete is primarily crane handled concrete, the fines content should be as for pumped concrete§
 Cement Min 300 kg/m³§
 CEM I 42.5 for close reinforcement and large dimensions, CEM I 52.5 for smaller dimensions (towers, chimneys)§

Workability: The best workability is achieved if a stiff plastic concrete contains a flow diameter of 35–40 cm and a low water content. Note particularly that a wall thickness below 14 cm can create a issue (plucking, anchorage of jacking rods etc.). The newly struck surfaces should be safeguarded as much as possible against wind, sunlight etc.

Article Source civilengineerblog.com

Read continue

~~~~~~~~~~~~~~~~~~~~~~~~

Published By

Rajib Dey

www.constructioncost.co

~~~~~~~~~~~~~~~~~~~~~~~~