Gary Polomark

Analysis of Bituminous Crack Sealants by Physicochemical Methods: Relationship to Field Performance

Bituminous crack sealants were analyzed by viscometry, fluorescence microscopy, infrared spectroscopy, thermogravimetry, modulated differential scanning calorimetry, and low-temperature tensile testing. The results indicate that sealants are blends of bitumen, oil, copolymer, and filler. Upon blending, these components produce a three-phase system that consists of a polymer-modified bitumen (PMB) matrix, a filler, and a filler-PMB interface. Spectroscopy and microscopy indicate that the PMB phase is rich in styrene-butadiene copolymer, that the filler is recycled rubber, sometimes mixed with calcium carbonate, and that the interface depends on the filler and the oil content in the sealant. The physicochemical methods were used to predict the short- and medium-term performance of sealant mixtures. The short-term performance predicted from viscometry and microscopy correlated well with the 1-year field performance of the sealants. Sealants showed two glass transition temperatures (Tg’s), and a reasonable correlation was also found between low Tg and medium-term performance in a wet-freeze climate. However, because Tg measurements do not account for stress relaxation and aging effects, correlation was not perfect.

The effect of thiocyanates on the hydration of portland cement at low temperatures

Abstract Sodium thiocyanate, potassium thiocyanate, ammonium thiocyanate, calcium thiocyanate, and lithium thiocyanate were added to Normal Type 10 portland cement in amounts of 1.5 and 3% (with respect to cement on weight basis) and cured at temperatures of 20, 0 and −5°C. The rate of development of heat of hydration, calcium hydroxide content and strength development were followed from a few hours up to 28 days. All thiocyanates increase the early rate of reaction of cement at 20°C. The most efficient early acceleration occurs with 3% Ca(SCN)2. The total heat of hydration in samples containing KSCN is about 30% more than that registered for the reference at 3 days. At 0°C, there was acceleration in the presence of thiocyanates and the heat of hydration was higher in all the samples containing thiocyanates. All thiocyanates accelerate hydration at −5°C with respect to the reference paste. The reference sample showed practically no hydration even up to 4 days as the water in the pores remained frozen. Some freezing occurred in the presence of NH4SCN, LiSN and 1.5% Ca(SCN)2. Calcium thiocyanate accelerates the hydration and strength development in the paste at all curing temperatures. It is the most effective thiocyanate for increasing strengths at low temperatures. After 28 days of curing at −5°C, the cement paste with 3% calcium thiocyanate attains a strength that is 74% of the strength of cement paste cured at 20°C. Sodium thiocyanate is also an effective accelerator and increases strength at low temperatures. The least effective thiocyanates with respect to the development of strengths at −5°C are LiSCN, KSCN and NaSCN at a dosage of 1.5%. A linear relationship exists between the amount of lime formed and strength, within the range of curing periods studied. However, when strength is compared at the same degree of hydration (in terms of lime formed), some pastes exhibit better strengths than others. The relative strengths, therefore, seem to be dependent more on the microstructure of the pastes than on the degree of hydration. At the same degree of hydration at −5°C, 1.5–3% Ca thiocyanate, or 3% Na, K and Li thiocyanates exhibit better strengths than those containing 1.5% Na, Li and K thiocyanates.

Application of DSC-DTA technique for estimating various constituents in white coat plasters

Abstract The DSC—DTA combination technique has been used to estimate CaSO 4 · 2H 2 O, Mg(OH) 2 , Ca(OH) 2 , CaCO 3 and MgO, comprising three white coat plasters. Unhydrated magnesium oxide could be estimated by converting it to Mg(OH) 2 by autoclaving. An equation is derived from which unhydrated MgO can be determined by substituting the estimated values for CaSO 4 · 2H 2 O, Mg(OH) 2 , Ca(OH) 2 and CaCO 3 . Estimated values of CaO, MgO and CaSO 4 · 2H 2 O obtained by the DSC—DTA technique correspond closely to those determined by chemical analysis.

Differential scanning calorimetric analysis of Ca(OH)2: Some anomalous thermal effects

Abstract An examination of the thermal characteristics of moist Ca(OH) 2 showed three peaks at 100, 400–450 and 250–300°C. The effect at 250–300°C was caused by calcium aluminate hydrate formed from the reaction of Ca(OH) 2 with the aluminum sample holder. This effect could be eliminated by using a sample holder made of gold.