L. Turanli

Use of ground clay brick as a pozzolanic material to reduce the alkali-silica reaction

The objective of this experimental study was to use ground clay brick (GCB) as a pozzolanic material to minimize the alkali-silica reaction expansion. Two different types of clay bricks were finely ground and their activity indices were determined. ASTM accelerated mortar bar tests were performed to investigate the effect of GCB when used to replace cement mass. The microstructure of the mortar was investigated using scanning electron microscopy (SEM). The results showed that the GCBs meet the strength activity requirements of ASTM. In addition, the GCBs were found to be effective in suppressing the alkali-silica reaction expansion. The expansion decreased as the amount of GCBs in the mortar increased.

Studies on blended cements containing a high volume of natural pozzolans

Abstract This paper presents the results of an investigation on the characteristics of laboratory-produced blended portland cements containing 55% by weight volcanic tuffs from Turkey. Volcanic tuffs from two different resources were used. Using different grinding times, particle size distribution, setting time, compressive strength, and alkali–silica activity of the blended cements were investigated and compared with reference portland cements ground for the same time period. For the compressive strength test, a superplasticizer was used to obtain mortar mixtures of adequate workability at a constant water-to-cement (w/c) ratio of 0.45. Compared to portland cement, the blended cements containing 55% pozzolan showed somewhat lower strengths up to 91 days when the grinding time was 90 min. However, at 91 days, blended cements and portland cements ground for 120 min showed similar strength. Moreover, blended cements containing 55% natural pozzolans showed excellent ability to reduce the alkali–silica expansion.

High-Volume Natural Pozzolan Concrete for Structural Applications

The authors present preliminary study results on concrete mixtures for structural applications containing high volumes of natural pozzolan (50% by total cementitious material mass). In high-volume natural pozzolan (HVNP) concrete mixture preparation, three different natural pozzolans were used from Turkish deposits. For purposes of comparison, two additional mixtures were also prepared with a high volume of low-calcium fly ash and granulated blast-furnace slag. Additionally, as a reference, a conventional portland cement concrete mixture was prepared. High-range water-reducing admixture dosage was determined for resistance to chloride-ion penetration, splitting-tensile strength, compressive strength, setting time, air content, and given slump. The suitability of studied high-volume natural pozzolan concrete mixtures for structural concrete applications were indicated by preliminary results with compressive strengths of 1.74 to 2.03 ksi (12 to 14 MPa) and 4.21 to 5.51 (29 to 38 MPa) at 3 and 28 days, respectively.

SETTING TIME: AN IMPORTANT CRITERION TO DETERMINE THE LENGTH OF THE DELAY PERIOD BEFORE STEAM CURING OF CONCRETE

Some precast concrete plants expose freshly made concrete elements to steam curing immediately after casting. This is detrimental to properties of the product; therefore, some delay prior to the steam curing process is beneficial. This paper contains the results of an investigation on the effects of various delay intervals selected based on initial setting time of concrete. Four different delay periods and two different steam curing periods at 80 °C (5 and 10 h) were used with two concrete types, namely C25 and C40. Compressive strength tests were performed at 1, 3, 7, 28, and 90 days. Setting time of the concrete was found to be an important criterion to determine the length of the delay periods.

Reduction in alkali–silica expansion due to steel microfibers

Abstract The alkali–silica reaction (ASR) produces an expansive gel that may cause cracking and displacement in concrete structures. Steel microfibers ranging from 1% to 7% by volume of cement mortar were incorporated to reduce the expansion and cracking. All specimens contained 5% of opal by weight of fine aggregates. The samples were cast and tested according to ASTM C-1260. A considerable reduction in expansion was observed for all steel microfiber-reinforced mortar specimens compared to the control specimens without fibers. The higher the fiber volume fraction, the lower the expansion. At constant fiber volume fraction, the expansion was further reduced when the curing time was extended from 1 day to 7 days due to an increase in the fiber-matrix interfacial bond strength.

Effects of retempering on consistency and compressive strength of concrete subjected to prolonged mixing

In this study, effects of prolonged mixing and four different retempering processes on some properties of fresh and hardened concrete, such as temperature, slump loss, and strength, were investigated. Two types of concrete mixtures with different compression strength having 15 cm initial slump were produced in a laboratory mixer. After mixing for 5 min at 20 rpm speed to ensure homogeneity, the mixing was continued at 4 rpm for a period of up to 4 h to simulate the prolonged agitation of ready-mixed concrete in truck mixers. Concrete samples were taken out of the mixer at the end of first, second, third, and fourth hour for estimating the effects of prolonged mixing on properties of fresh concrete. For restoring the initial workability, four different retempering methods were used and their effects on properties of concrete were investigated. Results show that compared to the untempered concrete mixtures, those tempered with solutions prepared by 3% or 4.5% solid superplasticizer by mass of retempering water had significantly less loss of 28-day compressive strength.

The effects of potassium and rubidium hydroxide on the alkali-silica reaction

Abstract Expansion of mortar specimens prepared with an aggregate of mylonite from the Santa Rosa mylonite zone in southern California was studied to investigate the effect of different alkali ions on the alkali–silica reaction in concrete. The expansion tests indicate that mortar has a greater expansion when subjected to a sodium hydroxide bath than in a sodium–potassium–rubidium hydroxide bath. Electron probe microanalysis (EPMA) of mortar bars at early ages show that rubidium ions, used as tracer, were present throughout the sample by the third day of exposure. The analysis also shows a high concentration of rubidium in silica gel from mortar bars exposed to bath solutions containing rubidium. The results suggest that expansion of mortar bars using ASTM C 1260 does not depend on the diffusion of alkali ions. The results indicate that the expansion of alkali–silica gel depends on the type of alkali ions present. Alkali–silica gel containing rubidium shows a lower concentration of calcium, suggesting competition for the same sites.

Assessing the Effects of Mechanical Preventive Measures on Alkali-Silica Reaction Expansion with Accelerated Mortar Bar Test

This paper presents a modification to the apparatus of the mortar bar test of ASTM C490 in order to assess and compare the influence of mechanical preventive measures in reducing alkali-silica reaction (ASR) expansion in concrete with respect to the traditional measures. For this purpose, reinforced mortar specimens with or without pre-stressing force applied were examined and the effects of the reinforcement ratio and pre-stressing force on ASR-induced expansion and cracking were studied through the accelerated mortar bar test method of ASTM C1260. The mechanical preventive measure was also compared with a traditional preventive measure by using fly ash. The results show that reinforcement and pre-stressing force play a role in limiting expansion and cracking due to ASR and that the developed test apparatus in this study can be used for measurements.