The shrinkage linear comparator is a precision apparatus used to measure length changes of hardened cement paste and mortar prismatic specimens. In this way it is possible to evaluate the drying shrinkage or expansion of hardened cementitious building materials. This testing equipment consists of aluminium alloy base with leveling feet, chrome plated columns with support for comparator with 0,001 mm scale intervals, as required by standards, and two stainless steel contact pins.

It has a standard calibration bar with reduced coefficient of thermal expansion, as required by standard. The rod calibration must be (160±1) mm long and it must present the ends of identical shape to that measurement pins.

The measurements must be made at least on three specimens. The size of specimens is: 40 mm x 40 mm x 160 mm.

The specimens must be packaged in a shrinkage mold with 6 special plugs in heads.

The mold shall consist of three horizontal compartments so that three prismatic specimens 40 mm × 40 mm in section and 160 mm in length can be prepared simultaneously.

The mold shall be made of steel with walls approximately 10 mm thick and it shall be constructed in such a manner as to facilitate the removal of molded specimens without damage. Each specimen must be equipped with measuring pins as provided by the standard.

These pins must be made of stainless steel or other hard material that does not react with the mortar. There are two types of pins that can be used: built in pins and projecting pins.

The length change shall be calculated in relation to the initial value (Lo) detected after 24 h. The deformation due to the movement should be expressed as the variation length (ΔL) to the length of comparison (Lg), in units of mm/m, expressed to the nearest 0.01 mm/m.

 

 

Comparator of length which measures the change in length of cement paste and mortar prismatic samples.Comparator of length which measures the change in length of cement paste and mortar prismatic samples.