Things to Remembered in Concrete Construction

by Prasad ·

Concrete construction is quite a popular topic in construction and there are lots to be remembered by the designers, supervisors, project managers, and contractors.

In this article were are concentrating on the important aspects that we should be aware of during the inception to completion of the project.

Each aspect is discussed in briefly highlighting the important facts to be remembered in concrete construction.

Let’s see what are standards related

Water Cement Ratio

W/C ratio = Water content / Cement Content

The most important ratio in concrete construction is the water-cement ratio. Generally, the water-cement ratio is kept at 0.5. However, it depends on the type of concrete mix.

Old days we decide on the water-cement ratio and did the mix design. In today’s construction, there are methods to modify the water-cement ration by addition admixtures.

Superplasitciser such as high range water reduces can be used to modify the water-cement ratio.

Cement Types used in Concrete Construction

According to the BS 8500-2:2015+A1:2016, there are for main types of cement namely CEM I, CEM II, CEM III and CEM IV.

Cement Type
CEM I	Portland Cement
CEM I	Sulfate- resisting Portland Cement
CEM II	Portland Silica Fume Cement
CEM II	Portland Limestone Cement
CEM II	Portland Slag Cement
CEM II	Portland Fly Ash Cement
CEM III	Blastfurnace Cement
CEM IV	Pozzolanic Cement

Under each category, there are more subcategories based on the content of the cement and other additions.

Characteristic Strenght of Concrete

The design strength considered for concrete is the characteristic strength. The definition of the characteristic strength of concrete could be referred from the article characteristic strength of concrete.

Slump Class – Consistence Classes

Measurement of the slump is a must in concrete construction.

Slump is the indication of the workability of the concrete. The following table indicates the typical slumps for concrete construction.

Flow diameter in accordance with EN 12350-5 / mm	Slump in accordance with EN 12350-2 / mm	Typical conditions of use
500	150	Concrete placed in dry conditions
560	180	Concrete placed by pumping or by tremie pipe in submerged conditions under water
600	200	Concrete placed by tremie pipe in submerged conditions under a support fluid

Mainly, there are two workability measurements such as slump classes and flow classes for concrete based on the method of measurement.

Slump Class

Slump Class	Slump tested in accordance with EN 12350-2 / mm
S1	10 to 40
S2	50 to 90
S3	100 to 150
S4	160 to 210
S5	≥ 220

Flow Class

Flow Class	Flow diameter tested in accordance with EN 12350-5 / mm
F1	≤ 340
F2	350 to 410
F3	420 to 480
F4	490 to 550
F5	560 to 620
F6	≥ 630

Target Slump and Allowable Tolerance

Target Slump in mm	≤ 40	50 to 90	≥ 100
Tolerance in mm	± 10	± 20	± 30

Target Flow Diameter and Allowable Tolerance

Target Flow diameter in mm	All Values
Tolerance in mm	± 40

Exposure Class

Exposure class is the classification of environmental and ground conditions where the structure is building. Depending on the exposure class, we select the factors connected with the durability of concrete.

The main code that we refer to for the durability of concrete is the BS 8500 latest version.

Classification of exposure class according to BS 5800-1:2015+A1:2016 is as follows.

X0 Class	No risk of corrosion or attack	For concrete without reinforcement or embedded metal.
XC Classes	Corrosion induced by carbonation	XC1 – dry or permanently wet; XC2 – wet, rarely dry; XC3 and XC4(XC3/4) – moderate humidity or cyclic wet and dry
XD Classes	Corrosion induced by chlorides other than from seawater	XD1 – moderate humidity, XD2 – wet, rarely dry, XD3 – cyclic wet and dry
XS Classes	Corrosion induced by chlorides from sea water	XS1 – exposed to airborne salt but not in direct contact with sea water, XS2 – permanently submerged, XS3 – Tidal, splash and spray zones
XF Classes	Freeze-Thaw attack	XF1 – moderate water saturation without de-icing agent, XF2 – moderate water saturation with de-icing agent, XF3 high water saturation without de-icing agent, XF4 – high water saturation with de-icing agent or sea
XA Classes	Chemical attack	XA1 – slightly aggressive chemical environment, XA2 – moderately aggressive chemical environment, XA3 – highly aggressive chemical environment
XAS Class	Chemical attach from sea water	Exposed to sea water

Chloride Class

When there is a risk of structure that having reinforcement or embedded steel expose to chloride environments, it is required to consider the chloride class as a durability requirement.

Depending on the exposure class that the structures are subjected to, the chloride class is selected.

For example, when the structure is building in an environment having exposure class XS or SD, the chloride class shall be selected as Cl 0.30. This means the chloride content shall not be greater than 0.3% by mass of cement or a combination of cement.

The following table indicates the data extracted from BS 5800-1:2015+A1:2016 is as follows.

Concrete Batching Tolerances

Batching tolerances when concrete volume less than one-meter cube shall be as follows as specified in BS 5800-1:2015+A1:2016.

These tolerances are shall be used with calibrated measuring equipment used in concrete construction.

Rate of Sampling to Assess the Conformity of Concrete

The rate of sampling depends on the quantity of concrete. The following table extracted from BS 5800-1:2015+A1:2016 indicates the sampling rates.

This table indicates the minimum rate and we may adjust the rate as required or project specification could be followed.

The following articles could also be referred to for more information on concrete.