Length Change Apparatus measures changes in length of cast prisms due to autoclave curing, alkali reactivity, and other causes not related to applied load. Methods are applicable to testing of hardened portland cement paste, mortar, concrete, or evaluation of hydraulic hydrated lime for structural purposes.

HM-250 and HM-250D Length Comparators are similar units for measuring length changes in 10in (254mm) specimens cast with special gage studs in the ends to fit the bottom and top anvils of the Comparator. Sensitive indicator with 0.0001in (0.0025mm) divisions measures specimen length. Recommended HM-250D has a quick-reading 0.5in (12.5mm) range LCD digital indicator with in/mm switch, RS-232 port, and replaceable 200 hour battery. Economy HM-250 has a 0.4in range mechanical dial indicator, which will convert to time-saving digital version with purchase of a digital indicator. Comparators include a heat treated, hardened Invar Reference Bar for exactly zeroing the dial indicator at regular intervals. Construction is a sturdy upright support attached to a solid base. Test specimens up to a 4x4x10in (102x102x254mm) cross section, but 1x1x10in (25x25x254mm) prisms are normal. Inquire for special adapter and shorter Invar Reference Bar if 5in (127mm) long prism samples are tested. Overall Comparator Dimensions: 11x11.5x17in (279x292x432mm), WxDxH.

HM-252 Cement Autoclave (ASTM C 151, AASHTO T 107, others) provides an accelerated means of estimating delayed expansion of portland cement caused by hydration of CaO and MgO. Test bars are exposed to controlled steam pressure and constant temperature. Unit is capable of pressures in the 60—350psi (0.4—2.4mPa) range and includes steam vessel, pressure regulator, pressure gauge (0—600psi x 5psi), air vent valve, power switches, a safety pop valve set at 350psi, MA-421F thermometer, wrench, and package of five gaskets. Replacement gaskets, and safety pop valves are available as accessories. Autoclave chamber is 6-1/8in (156mm) IDx16in (407mm) H. Overall Dimensions: 17x48x28in (432x1220x711mm), WxDxH; 1,800 Watts/15.7 amps maximum power demand on 115 VAC supplies. For use with 230V service, order TR-2000 transformer.

HM-254 Test Bar Holder (order separately) holds up to eight 1x1in (25x25mm) bars of 10in (254mm) gage length. Bars are held vertically above water level to expose all specimens to Autoclave steam.

Prism Molds, Gage Studs (ASTM C 490, AASHTO M 210, others): Prism Molds are corrosion- resistant steel (HM-258 is stainless) with base plate, removable partitions and end plates, designed to provide required length of 10in (254mm) between ends of gage studs cast in ends of bars. Dimensions from outside ends of studs (comparator gage contact points) are 11-5/8in (296mm); specimens are 11-1/4in (286mm) long. Select molds for specimen cross sections of 1x1in, 2x2in, or 3x3in. Molds for 5in (127mm) gage length specimens available. Package of ten stainless steel Gage Studs HM-268 are knurled and threaded, 1/4x13/16in (6.35x20.64mm) diameter x L.

HM-270 Mortar Bar Container (ASTM C 227), is stainless steel with tight fitting cover to seal in water vapor. Vertically supports up to 36 mortar bars in container with lower end above water surface. Box is 9x11x15.5in (229x279x394mm), LxWxH.