Smart Sensors Save Project QC/QA Costs
Concrete is the most widely used construction material in the world as its ingredients (aggregate, water, and cement) are readily available everywhere. The properties of hardened concrete are governed by various factors such as the mixture design and curing conditions.
Concrete is often custom ordered for specific projects based on the required strength, which is a critical parameter during various operations such as formwork removal and application of load. This is why accurate concrete strength evaluations are so important.
Why Traditional Concrete Strength Testing Doesn't Work
The most commonly used method to monitor the strength of concrete is break testing (breaking specimens that are poured and cured in the field subjected to the same curing conditions as for the concrete structure). Sometimes, cast-in-place concrete specimens are prepared by embedding plastic molds in the slab to achieve a better representation of real concrete strength.
This method is not efficient for two reasons:
- Results are not available right away (they must first be sent to a laboratory for analysis).
- Results are not accurate, as only one specimen is usually tested.
Even a couple of hours of delay and uncertainty in results have significant financial implications while the construction crew is waiting on the job site.
Among other non-destructive methods of strength measurement, the pull-out and Schmidt hammer tests are not reliable as they are greatly influenced by local material conditions.
The only non-destructive method that is widely accepted by the standards and building codes is the concrete maturity test. In this method, the strength is correlated with the concrete maturity which is a function of temperature history in field-cured concrete. ASTM C1074 and NEN 5970 describe three different standard specification for this method.
In-situ temperature monitoring, which is the key part of maturity method, is often performed using wired loggers or thermocouples connected to a data logger. These wired systems are installed prior to pouring concrete. After the concrete hardens, the temperature data is collected either using a handheld data logger or connecting the logger-box to computer. This data is then analyzed based on the concrete maturity concept to calculate concrete strength.
One of the main challenges of these systems making sure the wires don't get cut at the job site. Moreover, data collection and analysis is time consuming.
How Wireless Smart Sensors Reduce Project Costs
Recently, wireless mobile-based sensors (such as Giatec SmartRock) have been developed for more efficient approach to concrete temperature/maturity monitoring. Using these wireless mobile-based smart sensors can significantly reduce the time and thus the cost of concrete quality control. Here is how we calculated cost savings at an actual jobsite.
In a typical 40-storey high-rise concrete structure, 200 maturity meters are needed for real-time strength monitoring. Each SmartRock wireless temperature sensor helps save 20 minutes of installation time and 40 minutes of reading/analyzing time.
Assuming that the data from each sensor is collected on three separate occasions by a technician with an hourly cost of $50, the total labour cost savings in the quality control of this project approach $23,300. These savings easily justify an investment of $17,000 for wireless SmartRock sensors ($85 each).
In addition, costs are also significantly reduced as a result of the maturity method, which eliminates the need to break samples. In the example above, this alone accounted for $30K to $50K savings.
More importantly, by optimizing the construction schedule as the real-time strength monitoring enables project managers to save up to a day on early formwork stripping for each floor. Even in projects where the break test is mandatory, the maturity concept can be used to determine the optimum time at which the field specimens should be sent to a lab for the break test.
Considering all of these advantages, it's no surprise that more and more contractors are implementing the maturity method in their engineering practice. See SmartRock wireless sensors in action all over the world.