Different types of concrete mixes

Nominal Mixes: Earlier, specifications for concrete are set the ratios of cement and fine course aggregates. This mixes of fixed cement & aggregate ratio makes sure sufficient strength in concrete and it is termed as nominal mixes.

The strength of the nominal concrete for a specified workability fluctuates significantly because of the difference of mix components. In this type of mix, all the ingredients are prearranged and their proportions are given.

Nominal mix contains volumetric batching. It is mainly utilized for comparatively insignificant and simpler concrete works. Nominal mix concrete generally utilized for concrete of M-20 or lower.

Standard Mixes: The nominal mixes of fixed cement-aggregate ratio (by volume) differentiate greatly in strength and may leads to under or over-rich mixes. Due to this the least compressive strength is contained in various specifications. These mixes are described as standard mixes.

As per IS 456-2000 standard, the concrete mixes are divided into several grades like M10, M15, M20, M25, M30, M35 and M40. Here M denotes the mix and number to the number to the stipulated 28 day cube strength of mix in N/mm2.

The mixes of grades M10, M15, M20 and M25 conform roughly to the mix proportions (1:3:6), (1:2:4), (1:1:5:3) and (1:1:2) correspondingly.

Design Mixes: In these types of mixes, a designer indicates the performance of the concrete but the ratios of mixes are defined by the producer of concrete irrespective of the minimum cement content is set.

It is the most appropriate method for choosing the mix ratios with certain materials which contain comparatively distinct characteristics.

This method facilitates the formation of concrete keeping the proper properties most inexpensively. But this type of mix does not ensure the exact mix ratios for the standard performance.




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Published By
Rajib Dey
www.constructioncost.co
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Different types of bearings used in bridge structures

Bridge bearings stand for structural equipment or devices which are set up among bridge substructure and superstructure with the purpose of transmitting the functional load together with earthquake loads; wind loads; traffic loads; and superstructure self-weight.

Bridge bearings also allow for relative movements among superstructure and substructure, as for example, rotation movements and translational movements in horizontal and transverse direction.

Bearing is employed in building up the bridge structure. It is categorized as expansion bearings and fixed bearings. The first one allows for both translational and rotational movements while the second one allows for rotational and limited translational movements.

There are several types of bridge bearings which are frequently utilized in bridge construction. The details are given below :-

Various types of bearings for bridges: Sliding bearings, Rocker and pin bearings, Roller bearings, Elastomeric bearings, Curved bearings, Pot bearings, Disk bearings

Sliding Bearings for Bridges: Sliding bearing is made of two metal plates, generally stainless-steel plates, which slide corresponding to each other and therefore allows room for translational movement and lubricating material among them.

A friction force is produced in sliding bearing and it is enforced on substructure, superstructure and sliding bearing itself. So, it is necessary to arrange lubricant like polytetrafluoroethylene (PTFE) to reject generated friction.

As per guidelines by ASSHTO, the bridge span should be less than 15m to use sliding bearing in bridge structures. It is due to sliding bearing is not fully applicable if there is rotation movement in bridge.

While using sliding bearing, this span limitation can be avoided if it is employed in conjunction with other bearing types.

Rocker and Pin Bearings for Bridge Structures: Rocker stands for an expansion bearing that contains curved surface at the bottom. It adjusts translational movement and a pin at the top takes rotation movement into consideration.

Both rocker and pin bearings are vital parts of steel bridge structure. Rocker and pin bearing are taken into account when the bridge movement is suitably known and defined, because such bearings can allow for both translational and rotational movements in one direction only.

These bearings are susceptible to deterioration and corrosion, so inspection and maintenance should be performed on regular basis.

To get further details, go through the following article theconstructor.org

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Published By

Rajib Dey

www.constructioncost.co

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