Constructing multi-storey buildings involves critical steps like shoring and reshoring, making it imperative to monitor the early strength gain of concrete in the field. To achieve this, various techniques can be employed, each providing valuable data to control the timing of shoring/reshoring and form removal.
One method involves casting cylinders in the field, adhering to the ASTM C31/C31 M standard. These cylinders undergo curing under identical conditions as the concrete they represent. Lab testing, following the ASTM C39/C39M standard at specified ages, evaluates concrete compressive strength. This method ensures accuracy in assessing concrete strength in the field.
An alternative approach employs special cylinder molds attached to forms in the field. Following the ASTM C873/C873M standard, this method is limited to slabs with a concrete depth of 125 to 300 mm. The specimens, cast and cured under slab conditions, are tested at designated times. This technique aids in determining slab bearing capacity and, consequently, the optimal time for the removal of strips and shores.
Concrete maturity testing offers insights into compressive strength. Initially, a correlation between maturity and compressive strength is established for the specific concrete mixture intended for the project. ASTM C 1074 specifies the maturity test, providing a means to assess concrete strength based on project-specific mixtures.
Pullout tests provide an avenue to evaluate concrete compressive strength in the field. However, a correlation between compressive strength and pullout values must be established for the project-specific concrete mixture. Following ASTM C 900, this method aids in understanding the concrete’s strength development over time.
Similar to maturity and pullout tests, penetration resistance of hardened concrete can estimate compressive strength. Establishing correlations between compressive strength and penetration values for all concrete mixtures planned for the project is essential. Following ASTM C803/C803M, penetration resistance results can be easily converted to concrete strength, offering another reliable method for assessing early strength gain.
By employing these monitoring techniques, construction professionals can make informed decisions about critical construction steps, ensuring the success of multi-storey building projects.