Mixture Proportioning with Saturated Lightweight Aggregates

Mixture Proportioning with Saturated Lightweight Aggregates

The purpose of this form is to estimate the necessary replacement level of normal weight aggregates by their saturated lightweight counterpart to compensate for chemical shrinkage and avoid significant autogeneous shrinkage of a high-performance (low w/c ratio) concrete.

Even in higher w/c ratio concretes, this form will calculate the LWA/water needed to compensate for the chemical shrinkage so that all pores in the cement paste remain water-filled during hydration. Autogenous shrinkage is not typically an issue with w/c > 0.45 concretes. For these higher w/c ratio concretes, it may be more efficient and practical to supply curing water via conventional external curing methods.

For details, see the following papers:
Bentz, D.P., and Snyder, K.A., Protected Paste Volume in Concrete: Extension to Internal Curing Using Saturated Lightweight Aggregates, Cement and Concrete Research, Vol. 29, 1863-1867, 1999.

Bentz, D.P., Lura, P., and Roberts, J., A Methodology for Mixture Proportioning for Internal Curing, Concrete International, Vol. 27, No. 2, February 2005, pp. 35-40. pdf version

Please supply the following information (defaults provided)

w/c ratio

Cement factor for mixture proportions kg/m3 (lb/yd3)

Absorption (Desorption) of lightweight aggregate kg water/kg dry LWA (lb/lb) More information

Saturation of lightweight aggregates (0-1)

Chemical shrinkage of cement g water/g cement (lb water/lb cement) More information

Calculated Water Needed for Internal Curing

You do not need to change the fields provided below

Maximum expected degree of hydration of cement

Water needed for complete hydration and maintaining paste saturation kg water per m³ concrete (lb/yd³)

Recommended lightweight aggregate content is kg dry LWA/m³ concrete (lb/yd³)

The indicated lightweight aggregate should be used to replace an equivalent volume of normal weight aggregates and should be added to the mixture in pre-wetted conditions. Remember that the water in the saturated lightweight aggregates should not be counted as part of the mix water (i.e. it is in addition to the water needed for the mixture proportions)

Further considerations are that the lightweight aggregates should have a high fineness modulus to distribute this extra hydration water as evenly as possible throughout the concrete and that it should be of an adequate strength and shape to not adversely influence the rheological and strength properties of the final concrete.

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