# Possibilities of K-Value Determination for Active Admixtures with Respect to Durability

## TL;DR

This paper explores how to calculate k-values for concrete admixtures by considering durability factors like water penetration and carbonation depth.

## Contribution

The study introduces a method to determine k-values by incorporating durability factors, which were previously ignored.

## Key findings

- A mathematical model using regression analysis was developed to calculate k-values based on durability factors.
- The model achieved a high coefficient of determination (0.9855) for water seepage depth but lower for carbonation depth.
- Optimization techniques were used to minimize the difference between actual and calculated durability measurements.

## Abstract

This paper discusses the possibility of determining k-values for active admixtures concerning durability factors such as the depth of penetration of water under pressure and the depth of carbonation of cement mortars with fly ash. The k-value considers the use of active admixtures in concrete when calculating the water/cement ratio and the equivalent amount of binder. Currently, only the effect of the active admixture on the compressive strength of concrete and cement mortars is considered when determining the k-value, but not the effect of the active admixture on durability. To account for the influence of durability factors on the determination of the k-value, the mathematical functions of the property, dependent on the water/cement ratio and the age of the cement mortar, were constructed using regression analysis. From the determined functions, it was then possible to use an optimisation problem to determine the k-value so the difference between the actual measurement and calculated depth of pressure water seepage or carbonation was as small as possible. A high coefficient of determination of 0.9855 was achieved for the pressure water seepage depth function, but the coefficient of determination for the carbonation depth was lower.