Everything You Need to Know About The Compressive Strength of Concrete

Compressive Strength of Concrete Definition

A concrete compression test measuring the resilience of hardened concrete is defined as the compressive strength of concrete. It is measured by analysing the concrete’s ability to withstand loads that may compress it.

Importance of Strength Test of Concrete

It is important to carry out a check for the compressive strength of concrete to find out whether the concrete mixture curated on-site meets the requirements of the strength mentioned in the job specification.

The project manager gets an idea about the characteristics of the concrete as factors like strength, consistency, unit weight, air content, and temperature are measured through concrete compression tests. Consistent performance of these tests can help the manager detect changes that may affect its long-term performance.

Methods for Compressive Strength Test of Concrete

There are many other methods and tests to check the compressive strength of concrete. Let’s take a look at a few of these approaches:

1) Rebound Hammer or Schmidt Hammer

In this method, a hammer is activated by a spring release mechanism, striking a plunger to drive through the concrete's surface. A value between 10 and 100 is assigned to the rebound distance between the hammer and the concrete surface. The strength of the concrete is then associated with this measurement. 

This method of checking the compressive strength of concrete is relatively easy to use. However, pre-calibration using cored samples is needed for accurate results. Moreover, although this can be done directly on-site and helps save time, the results can be led astray by surface conditions or other factors.

2) Penetration Resistance Test

To complete a penetration resistance test, a small pin or probe is driven into the surface of the concrete through a device. The strength of the in-place concrete is linked with the force required to pierce the surface and the depth of the hole.

This method of checking the compressive strength of concrete,  also requires pre-calibration using several concrete samples to provide accurate results. Although it is easily carried out on-site, the measurements are affected by surface conditions and forms of aggregates used.

3) Ultrasonic Pulse Velocity

This method calculates the speed of a vibrational energy pulse across a slab. The ease with which this energy passes through the slab yields data on the density, elasticity, and resistance to deformation or stress of the concrete. The strength of the slab is then determined using this data.

The technique is non-destructive and can identify faults like cracks and honeycombing in the concrete. However, the results are majorly influenced by reinforcements, aggregates, and moisture content of the concrete component and require pre-calibration using several samples.

4) Pullout Test

The fundamental idea behind this test is to pull the concrete using a metal rod that has been inserted or cast in place. The compressive strength of concrete is associated with the pulled conical form and the force needed to draw out the concrete.

While this method can be effectively carried out on old and new construction sites alike, it involves destroying the concrete. The compressive strength test of concrete also requires an extensive amount of samples to provide exact results.

5) Drilled Core

In this method, the pouring area is covered with cylinder moulds. These moulds, which remain in the slab, are filled with fresh concrete. These specimens are removed and squeezed for strength once solidified.

Because the concrete is treated to the same curing circumstances as the in-place slab, as opposed to field-cured specimens, it is thought to be more accurate. However, this kind of construction involves compromising the slab's structural stability and the data must be obtained in a lab. After that, the holes must be fixed where they were.

6) Cast-in-place Cylinders

In this method the concrete that has hardened is removed from the slab using a core drill. To measure the strength of the in-situ concrete, these samples are subsequently compacted in a machine.

Because the concrete that is tested for strength has been exposed to the same thermal history and curing circumstances of the in-place slab, these samples are considered more precise than field-cured models. However, this method of checking the compressive strength of concrete is also destructive and requires a lab for data measurement. 

7) Wireless Maturity Sensors

This method is based on the notion that the temperature history of the concrete's hydration is closely related to the quality and strength of the concrete. Before pouring, wireless sensors are mounted on the rebar and inserted into the concrete formwork. 

The sensor gathers temperature information, which is wirelessly transferred to any smart device and stored in an app. Based on this data and the maturity equation set up in the app, the compressive strength of the concrete is calculated.

The Calculation for the Compressive Strength Test of Concrete

In understanding the compressive strength of concrete, the calculation for the strength test is pivotal. This process involves determining the force needed to break a concrete cylinder, resulting in a compressive strength value. Engineers use precise mathematical formulas to assess the material's ability to withstand pressure, ensuring structures meet safety standards.

As cities grow, understanding and using these strength values is key to making structures safe and long-lasting. Engineers and builders rely on these precise calculations to ensure buildings across the country can withstand various situations that have a direct impact on their strength.