Tomislav Matusinović

Porosity–strength relation in calcium aluminate cement pastes

Abstract The compressive strength and the volume porosity of calcium aluminate cement pastes have been studied in order to connect their relationship. The influence of mass fraction of lithium carbonate on compressive strength and porosity of calcium aluminate cement (CAC) has been investigated at different water–cement (w/c) ratios. The functions proposed in the literature for different technical materials were tested on obtained strength and porosity data. Those functions have been a base for further development of more general functional dependence of strength and porosity for cement materials. Thus, we propose the following equation to relate the strength and porosity for CAC pastes: σ=σ P 0 1− P P 0 2

LITHIUM SALTS AS SET ACCELERATORS FOR HIGH ALUMINA CEMENT

Abstract The set of high alumina cement (HAC) may be considerably influenced by addition of small quantities of alkali metal salts. The influence of concentration of the salt, chemical nature of anion and the type of alkali metal cations have been studied. The measurements of flexural and compressive strength of HAV and HAC with lithium and other alkali metal salts have been made. The lithium cation has greater effect on the setting time than other alkali cations. The effect of hydroxyl ion on setting time is greater than the effect of other investigated anions. Along with rapid setting, lithium salts cause the strength development at early ages. The integral analyses of the results have been made in order to test the process of hardening. The process obeys a simple first-order reaction rate in the period of 6 h after first appearance of the strength. The action of lithium-containing setting accelerators is based on a shortening of the induction period, while they have no effect on the rate of hardening.

Copolymerization and Copolymers of Acrylonitrile with Some Brominated Phenylmaleimides

Abstract Acrylonitrile (AN) was copolymerized with N-(4-bromophenyl)-maleimide (BPMI) or N-(2,4,6-tribromophenyl)maleimide (TBPMI) in toluene solution using azobisisobutyronitrile as the free radical initiator. The monomer reactivity ratios were found to be for BPMI (M1)-AN (M2), r1=0.44 ± 0.082 and r2 = 1.82 ± 0.125, and for TBPMI (M1)-AN (M2), r1 = 0.053 ± 0.051 and r2 = 4.71 ± 0.275. The e and Q values were also calculated. The course of copolymerization to high conversion is characterized by a remarkable decrease of the initial reaction rate as well as of overall conversion as the fraction of brominated monomer in the monomer mixture is increased. However, these values are somewhat higher when BPMI is used as a comonomer. The resulting copolymers show a higher thermal stability than that of polyacrylonitrile, and the glass transition temperature increases markedly with increasing BPMI or TBPMI content.

Alkali metal salts as set accelerators for high alumina cement

Abstract The effect of alkali metal salts on the setting time of high aluminia cement (HAC) has been studied. The influence of concentration of the salts, chemical nature of anion and the type of alkali metal cation have been investigated. The results of the research indicate that alkali metal salts are set accelerators of HAC. The lithium cation has more effect on the setting time than other alkali cations because of its ability to form tetrahedral symmetry while the others will form the octahedral type. Lithium salts remove the nucleation barrier, caused by an initially fast precipitation. The influence of pH in mixing water is not important. The effect of hydroxyl group is greater than effect of other investigated anions due to the replacement leading to a further centre for oxobridge formation. The lithium salts cause decreasing of flexural and compressive strength of HAC mortars but also cause the strength development at early ages.

Alternating Copolymerization of Styrene and N-(4-Bromophenyl)Maleimide

Abstract Free radical copolymerization of styrene (St) and N(4-bro-mophenyl)maleimide (4BPMI) in dioxane solution gave an alternating copolymer in all proportions of feed comonomer compositions. The monomer reactivity ratios were found to be r 1, = 0.0218 ± 0.0064 (St) and r 2, = 0.0232 ± 0.0112 (4BPMI), and the activation energy of the copolymerization reaction for the equimolar ratios of comonomer was E a, = 51.1 kJ/mol. The molecular weights of the copolymers obtained are relatively high, the T gs showed similar values (490 K), and the thermal stability is higher than that of polystyrene. The initial rate of copolymerization depends on the total concentration of the comonomers and the maximum occurred at higher 4BPMI mol fractions; however, the overall conversion is highest at equimolar comonomer composition. It has been shown that a charge-transfer complex participates in the process of copolymerization. The initial reaction rate was measured as a function of the monomer molar ratios, and the partici...