Properties of alkali-activated mortar and concrete using lightweight aggregates

This study reports the testing of 12 alkali-activated (AA) mortars and six AA concretes using lightweight aggregates. These tests aimed to explore the significance and limitations of the development of lightweight AA mortar and concrete. Ground granulated blast-furnace slag, which was used as source material, was activated by sodium silicate powder. The main parameter investigated was the replacement level of lightweight fine aggregates to the natural sand. The effect of the water–binder ratio on the compressive strength development was also studied in AA mortars. Initial flow and development of compressive strength were recorded for the lightweight AA mortar. For the lightweight AA concrete, many factors were measured: the variation of slump with elapsed time, the development of compressive strength, splitting tensile strength, moduli of rupture and elasticity, stress–strain relationship, bond strength and shrinkage strain. Test results showed that the compressive strength of AA mortar decreased linearly with the increase of the replacement level of lightweight fine aggregates, regardless of the water–binder ratio. The compressive strength of AA concrete, however, sharply decreased when the replacement level of lightweight fine aggregates exceeded 30%. In particular, the increase in the discontinuous grading of lightweight aggregate resulted in the deterioration of the mechanical properties of AA concrete.     

Low-volume wet-process sprayed concrete: pumping and spraying

This paper, which reports on part of a three-year research project into wet-process sprayed concrete for repair, examines the influence of rheology on the pumping and spraying of fine concretes. The performance of ten laboratory-designed fine concretes were examined using a rotational viscometer, the slump test, a build test and a vane shear strength test. Visual grading and a sorptivity test were used to quantify the degree of reinforcement encasement which is a crucial factor in long term performance. Taken together, these tests form a rheological audit of each concrete which can help guide the design of sprayable, but also durable concretes. The two-point apparatus was successful for determining the flow resistance and torque viscosity of fine aggregate concretes, including those with air entrainment. The vane shear strength test was successful in providing an instantaneous reading of the shear strength of the concretes and is compared with their slump. The concretes were pumped and sprayed through a piston pump to assess their suitability and to measure their adhesion to a substrate by build thickness. This value is a measure of sprayability and is converted into values of maximum shear and tensile stress which are then compared with the workability parameters in order to determine their inter-relationship. These relationships are also compared with those obtained from a separated study of mortars. On its own, the sorptivity test did not accurately assess the encapsulation of the reinforcement. However, when considered with a visual grading of the cores, a more reliable indication can be obtained of the potential durability of the finished concrete, as well as the degree of encapsulation of the reinforcement. We demonstrate the conflict in selecting mix proportions that satisfy requirements for both installation and product quality.     

A study on the effect of nano silica on compressive strength of high volume fly ash mortars and concretes

This paper presents the effect of nano silica (NS) on the compressive strength of mortars and concretes containing different high volume fly ash (HVFA) contents ranging from 40% to 70% (by weight) as partial replacement of cement. The compressive strength of mortars is measured at 7 and 28 days and that for concretes is measured at 3, 7, 28, 56 and 90 days. The effects of NS in microstructure development and pozzolanic reaction of pastes containing above HVFA contents are also studied through backscattered electron (BSE) image and X-ray diffraction (XRD) analysis. Results show that among different NS contents ranging from 1% to 6%, cement mortar containing 2% NS exhibited highest 7 and 28 days compressive strength. This NS content (2%) is then added to the HVFA mortars and concretes and the results show that the addition of 2% NS improved the early age (7 days) compressive strength of mortars containing 40% and 50% fly ash by 5% and 7%, respectively. However, this improvement is not observed at high fly ash contents beyond 50%. On the other hand, all HVFA mortars exhibited improvement in 28 days compressive strength due to addition of 2% NS and the most significant improvement is noticed in mortars containing more than 50% fly ash. In HVFA concretes, the improvement of early age (3 days) compressive strength is also noticed due to addition of 2% NS. The BSE and XRD analysis results also support the above findings.     

Compressive strength development of binary and ternary lime–pozzolan mortars

This study considers the compressive strength development of broad range of hydraulic lime mortars prepared with a range of commercially available alumino-silicate by-products and modern pozzolanic additions. Specifically this paper considers the effect of mineral addition selection, binary and ternary combinations, pozzolan content and the effect of curing conditions on the compressive strength development of hydraulic lime based mortars. The study was undertaken as the initial phase of a broader investigation considering the feasibility of producing modern, sustainable hydraulic lime–pozzolan concretes with comparable strengths to Portland cement based concretes. The aim of the initial phase was to identify a small number of additions, and combinations thereof, which would result in a structural strength lime–concrete when scaled up from mortars to concretes.In the absence of a definitive source of information on the mechanical properties of hydraulic-lime mortars prepared with binary and ternary combinations of alumino-silicate by-products, 22 combinations consisting of Natural Hydraulic Lime (NHL5) and a range of possible additions, identified from historical and current practice, were prepared. The results have shown that combining an eminently-hydraulic NHL5 with silica fume and ground granulated blastfurnace slag can produce mortars with a 28-day compressive cube strength of around 28 N/mm², at a water-to-binder (w/b) ratio of 0.5. This is eight times the strength of an equivalent mortar prepared with NHL5 alone and broadly speaking comparable with that of low-heat cementitious mortars. The contribution of the pozzolanic reaction to the strength of hydraulic lime mortars is discussed for a range of alumina-silicious materials and combinations thereof.     

Influence of sand grading,fines content and clay content on properties of sand-gypsum mortar

The paper summarizes a series of tests carried out on gypsumsand mixes—made of crushed dolomitic stone sand and retarded hemihydrate—seeking answers to the following questions:

1. Does the sand grading affect mortar properties?
2. How do the fines (fraction passing No. 100 sieve) affect mortar properties?
3. How does the clay content influence the properties of mortars?

Evaluation criteria for the hardened mortars were: flexural and compressive strength, hardness and linear change.     

改性石膏对磷渣混凝土强度激发作用的研究

本文通过实验手段,研究了改性石膏对磷渣混凝土强度的影响,并结合XRD、SEM分析改性石膏-磷渣混凝土水化产物的结晶形态和矿物组成。结果表明：在磷渣粉掺量相同的情况下,加入天然石膏、120℃烧石膏、550℃烧石膏激发剂后,水化产物主要是水化硅酸钙、钙矾石,因此,磷渣混凝土抗压强度有了不同程度的提高,其中外掺6%的550℃烧石膏作激发剂的磷渣混凝土抗压强度最大。     

A study of the workability of natural hydraulic lime mortars and its influence on strength

Lime mortars are currently used for both repairs to historic buildings and new construction. An important mortar property is workability. Lime mortars are often described as highly workable, however, due to the many variables contributing to workability, this is difficult to quantify. Workability largely depends on water content, and this will greatly affect compressive and flexural strengths, which in turn will determine the overall quality and durability of a mortar. The objective of this paper is to examine the relationship between workability and strength of naturally hydraulic lime (NHL) mortars in order to optimize their properties for a more efficient use in building. To this aim, mortars of several hydraulic strengths were mixed with different water contents in order to vary flow diameters and characterize workability. Compressive and flexural strength were then tested to measure the effect of the initial flow on the strength of the hardened mortar. This paper demonstrates that NHL 3.5 and 5 mortars require a flow value close to that of 185 mm prescribed by the European standards whereas NHL 2 mixes require a significantly lower value. This paper concludes that one universal flow value is inadequate when trying to optimize strength of NHL mortars and that, in order to optimize strength, mortars should be mixed to attain a different flow diameter for each hydraulic strength. However, other properties such as bond strength and water retention need to be considered before unique flow diameters are prescribed to lime mortars of different hydraulic strengths.      

Properties of lightweight aggregates produced with cold-bonding pelletization of fly ash and ground granulated blast furnace slag

Pelletization is a worldwide process used in producing artificial aggregates although its usage is not common in Turkey. In this study, lightweight aggregates (LWAs) were manufactured through cold-bonding pelletization of ground granulated blast furnace slag (G) and two types of fly ash with different finenesses (Fly ash A and B). Ordinary Portland cement (PC) was used as a binder at varying amounts from 5 to 20 % by weight. A total of 20 cold-bonded lightweight aggregates were produced at room temperature with different combinations of PC, FA and/or G. The hardened aggregates were tested for specific gravity, water absorption, and crushing strength. Thereafter, lightweight concretes (LWCs) were produced with water to cement ratio of 0.50 and a cement content of 400?kg/m³ by using such lightweight aggregates. The hardened concretes were tested for compressive strength at 28 and 56?days to explore the effect of aggregate types on the compressive strength development. Test results revealed that the amount of cement content had a significant effect on the strength of LWAs which in turn governed the variation in compressive strength of the LWCs. The highest 28 and 56-day compressive strengths of 43 and 51?MPa, respectively were achieved for the concretes including LWAs produced from the blend of 40 % slag, 40 % FA-A and 20 % PC.     

Influence of cement kiln dust on the physical properties of calcium lime mortars

This work investigates the influence of cement kiln dust (CKD) on the properties of mortars made with a non-hydraulic binder of high available-lime content (calcium lime—CL), in order to further recycle industrial waste. Physical properties of CKD-CL90 mortars with increasing CKD content were compared to those of feebly-hydraulic lime (NHL2) and CL90 mortars. This paper concludes that, despite the CKD in this study being partially inert, the abundant reactive, free lime provided by the CL90 binder has enabled formation of hydration products. The strength development, rising proportionally to the amount of CKD when addition is over 5%, and the reduction in porosity/suction of the CKD/CL90 mixes, support the occurrence of hydraulic set. The high alkalinity of the CKD/CL90 system; the high specific surface of the CKD particles and the presence of amorphous reactive silica further support the presence of hydraulic set. Results evidenced that CKD addition significantly increased the mortar’s water demand simultaneously enhancing compressive strength and bulk density, and decreasing porosity and capillary suction. These effects can be ascribed to both the gain of packing density induced by the CKD particles, and the formation of hydration phases within pores and the space originally filled with water. Finally, this work concludes that the physical properties of CKD/CL mortars including at least 20%CKD are comparable to those of feebly hydraulic lime mixes, however, fracturing by shrinkage (due to high water demand) and damage related to sulphur, chlorine and alkali content need to be investigated before CKD/CL mixes are advised for application.     

Performance of Portland limestone cements in mortar prisms immersed in sulfate solutions at 5 °C

The results of a test programme to investigate the sulfate resistance of mortars, immersed up to 12 months at 5 °C in magnesium sulfate and sodium sulfate solutions, is described. The mortars were prepared from four cements; a Portland cement, a sulfate-resisting Portland cement and two Portland limestone cements containing 15% by mass of an oolitic limestone and a carboniferous limestone. The mortar specimens were subject to BS 5328 Class 4A and 4B sulfate exposure conditions. These are the highest classes for concretes prepared using sulfate-resisting Portland cement (SRPC) before surface protection is required and are two and three classes higher than those recommended for concretes prepared using Portland cement (PC) and Portland limestone cement (PLC), respectively. Two free water-cement ratios were used, 0.5 and 0.75. Performance was monitored by visual assessment, expansion and changes in flexural and compressive strengths.At a free water-cement ratio of 0.75, the PC mortars and PLC mortars exhibited visually very severe attack with the former showing expansion and reductions in strength, and the latter mainly reductions in strength. At a free water-cement ratio of 0.50 both the PC mortars and PLC mortars showed slight/moderate to severe visual attack, the degree of deterioration appearing slightly greater in the PLC mortars, more especially those made with oolitic limestone. The PLC mortars also exhibited reductions in compressive failure load. The SRPC mortars exhibited little visual deterioration, no expansion, a small increase in flexural strength and no significant reductions in compressive strength. At a free water-cement ratio of 0.75 substantial amounts of thaumasite, together with ettringite was present in the surface layers of the deteriorated PLC mortars whilst ettringite was present in the surface layers of the deteriorated PC mortars. It is concluded that mortars made with a PC with a C₃A content of about 10% by mass were broadly similar in their vulnerability to sulfate attack at 5 °C as PLC mortars containing 15% limestone by mass, although the mode of attack was different.     

Effects of mineral admixtures on fresh and hardened properties of self-compacting concretes: binary,ternary and quaternary systems

The paper presented herein investigates the effects of using supplementary cementitious materials in binary, ternary, and quaternary blends on the fresh and hardened properties of self-compacting concretes (SCCs). A total of 22 concrete mixtures were designed having a constant water/binder ratio of 0.32 and total binder content of 550 kg/m³. The control mixture contained only portland cement (PC) as the binder while the remaining mixtures incorporated binary, ternary, and quaternary cementitious blends of PC, fly ash (FA), ground granulated blast furnace slag (GGBFS), and silica fume (SF). After mixing, the fresh properties of the concretes were tested for slump flow time, L-box height ratio, V-funnel flow time, setting time, and viscosity. Moreover, compressive strength, ultrasonic pulse velocity, and electrical resistivity of the hardened concretes were measured. Test results have revealed that incorporating the mineral admixtures improved the fresh properties and rheology of the concrete mixtures. The compressive strength and electrical resistivity of the concretes with SF and GGBFS were much higher than those of the control concrete.     

Performance of metakaolin concrete at elevated temperatures

An experimental investigation was conducted to evaluate the performance of metakaolin (MK) concrete at elevated temperatures up to 800 °C. Eight normal and high strength concrete (HSC) mixes incorporating 0%, 5%, 10% and 20% MK were prepared. The residual compressive strength, chloride-ion penetration, porosity and average pore sizes were measured and compared with silica fume (SF), fly ash (FA) and pure ordinary Portland cement (OPC) concretes. It was found that after an increase in compressive strength at 200 °C, the MK concrete suffered a more severe loss of compressive strength and permeability-related durability than the corresponding SF, FA and OPC concretes at higher temperatures. Explosive spalling was observed in both normal and high strength MK concretes and the frequency increased with higher MK contents.     

The use of oil shale ash in Portland cement concrete

An experimental investigation was undertaken to study the potential use of Jordanian oil shale ash (OSA) as a raw material or an additive to Portland cement mortar and concrete. Different series of mortar and concrete mixtures were prepared at different water to binder ratios, and different OSA replacements of cement and/or sand. The compressive strength of mortar and concrete specimens, cured in water at 23 °C, was determined over different curing periods which ranged from 3 to 90 days. The results of these tests were subjected to a statistical analysis. Equations were developed by regression analysis techniques to relate the effect of batch constituents on the strength developments of OSA mortars and concretes. The models were checked for accuracy by comparing their predictions with actual test results.The obtained results indicated that OSA replacement of cement, sand or both by about 10% (by wt) would yield the optimum compressive strength, and that its replacement of cement by up to 30% would not reduce its compressive strength, significantly. It was found that OSA on its own possesses a limited cementitious value and that its contribution to mortar or concrete comes through its involvement in the pozzolanic reactions. The statistical model developed showed an excellent predictability of the compressive strength for mortar and concrete mixes.     

Influence of the aggregate quality on the physical properties of natural feebly-hydraulic lime mortars

This paper examines the influence of the shape, average size and calcite content of the aggregate on strength, porosity, water absorption, density and capillary suction of natural feebly-hydraulic lime (NHL 2) mortars. Four types of aggregate were analysed in order to determine calcite content, particle shape and average particle size. Four different mortar mixes were then designed and produced using each of the aggregate types and NHL 2 as a binder. The mixing and curing as well as the aggregate:binder proportions were kept constant in order to attribute variation of mortar properties to the quality of the aggregate. The results suggest that an increase in the aggregate’s calcite content lowers the flexural and compressive strength of the mortar. This study also determined that sharp aggregate as well as aggregate with a small average particle size tends to increase the mechanical strength and bulk density of a mortar simultaneously reducing porosity, water absorption and capillary suction. Furthermore, this paper concludes that aggregates containing particles of a wide size range will also increase the mechanical strength and bulk density of the hardened mortar diminishing porosity, water absorption and capillary suction.      

Mechanical and durability properties of ternary concretes containing silica fume and low reactivity blast furnace slag

In this study, the effect of incorporation of silica fume in enhancing strength development rate and durability characteristics of binary concretes containing a low reactivity slag has been investigated. Binary concretes studied included mixes containing slag at cement replacement levels of 15%, 30% and 50% and mixes containing silica fume at cement replacement levels of 2.5%, 5%, 7.5% and 10%. Ternary concretes included combinations of silica fume and slag at various cement replacement levels. The w/b ratio and total cementitious materials content were kept constant for all mixes at 0.38 and 420 kg/m³ respectively. Concrete mixes were evaluated for compressive strength, electrical resistance, chloride permeability (ASTM C1202 RCPT test) and chloride migration (AASHTO TP64 RCMT test), at various ages up to 180 days.The results show that simultaneous use of silica fume has only a moderate effect in improving the slow rate of strength gain of binary mixes containing low reactivity slag. However it improves their durability considerably. Using appropriate combination of low reactivity slag and silica fume, it is possible to obtain ternary mixes with 28 day strength comparable to the control mix and improve durability particularly in the long term. Ternary mixes also have the added advantage of reduced water demand.     

Effects of particle size of treated CRT funnel glass on properties of cement mortar

Over the last decade, new types of display technologies have increasingly replaced cathode ray tube (CRT) displays leading to an increase in the disposal of discarded old CRT monitors and TV sets. The present study is a further development of our previous work to explore the effects of using different size fractions of crushed CRT glass as 100 % substitution of sand in cement mortar. A range of cement mortar mixes were prepared and the tests conducted included table flow (fluidity), mechanical strength, drying shrinkage, alkali–silica reaction (ASR) expansion and toxicity characteristic leaching procedures. Generally, the results obtained for the CRT glass-based cement mortars were comparable to those of the beverage glass mortars except the hardened density due to the presence of lead in the CRT glass. Decreasing the particle size of the CRT glass led to a decrease in fluidity, compressive strength and water absorption. However, the use of finer glass particles slightly improved the flexural strength and reduced the risk of expansion due to ASR due to its pozzolanic reaction. The experimental results indicated that treated CRT glass can be utilized as 100 % replacement of sand in cement mortar regardless of its particle size.     

Properties of self-compacting mortars with binary and ternary cementitious blends of fly ash and metakaolin

The link between flow properties and the formulation is actually one of the key-issues for the design of self-compacting concretes (SCC). As an integral part of a SCC, self-compacting mortars (SCMs) may serve as a basis for the design of concrete since the measurement of the rheological properties of SCCs is often impractical due to the need for complex equipment. This paper discusses the properties of SCMs with mineral admixtures. Portland cement (PC), metakaolin (MK), and fly ash (FA) were used in binary (two-component) and ternary (three-component) cementititios blends. Within the frame work of this experimental study, a total of 16 SCMs were prepared having a constant water-binder (w/b) ratio of 0.40 and total cementitious materials content of 550 kg/m³. Then, the fresh properties of the mortars were tested for mini-slump flow diameter, mini-V-funnel flow time, setting time, and viscosity. Moreover, development in the compressive strength and ultrasonic pulse velocity (UPV) of the hardened mortars were determined at 1, 3, 7, 14, and 28 days. Test results have shown that using of FA and MK in the ternary blends improved the fresh properties and rheology of the mixtures when compared to those containing binary blends of FA or MK.     

Effects of thermal and mechanical activation methods on compressive strength of ordinary Portland cement–slag mortar

Activation methods and curing regimes have crucial effects on the strength of mortars and concretes. The objective of this investigation is to examine the early and later compressive strength of activated ordinary Portland cement (OPC)–ground granulated blast-furnace slag (GGBFS) mortars and identify the most effective activation technique. The methods of activation used were thermal, mechanical and thermal–mechanical combined. Two curing regimes were adopted and five groups of mortars were prepared. It was observed that OPC–GGBFS mortars have greater sensitivity to OPC mortars against the curing regimes. However, the study revealed that there was no particular activation method which when used gave the best results for both early and later strengths and did not cause strength loss. It also proved that the most effective activation method for early strength is a combination of both the thermal and mechanical, while for later strengths, none of the activation methods was recommended.     

High strength concrete containing natural pozzolan and silica fume

Various combinations of a local natural pozzolan and silica fume were used to produce workable high to very high strength mortars and concretes with a compressive strength in the range of 69–110 MPa. The mixtures were tested for workability, density, compressive strength, splitting tensile strength, and modulus of elasticity. The results of this study suggest that certain natural pozzolan–silica fume combinations can improve the compressive and splitting tensile strengths, workability, and elastic modulus of concretes, more than natural pozzolan and silica fume alone. Furthermore, the use of silica fume at 15% of the weight of cement was able to produce relatively the highest strength increase in the presence of about 15% pozzolan than without pozzolan. This study recommends the use of natural pozzolan in combination with silica fume in the production of high strength concrete, and for providing technical and economical advantages in specific local uses in the concrete industry.     

Flexural bond strength of natural hydraulic lime mortar and clay brick

This paper measures the bond strength of natural hydraulic-lime (NHL) mortars, to further characterise their properties and enhance their use in building. An additional objective is to correlate bond strength with mortar hydraulicity, water content, workability and water retention, to develop mortars of high bond strength that would improve the quality of masonry. To this aim, the flexural bond strength of masonry, built with mortars of three hydraulic strengths-each including the water amount required to attain three specific flows (165, 185 and 195 mm), was measured with the bond wrench test. The results suggest that NHL mortars possess high water retention, and this enables a strong bond that compares well to that of Portland cement and cement/lime mortars. The results also indicate that bond strength is not determined by the binder’s hydraulic strength, but it increases proportionally to the mortar’s water retention. The paper concludes that for the NHL5 mortars, the 185 mm flow results in the strongest bond, simultaneously providing the highest water retention and best workability. However, for the lower strengths (NHL 2 and NHL 3.5 mortars), the water content required to attain the flows that provide an optimum workability (165 and 165–185 mm, respectively) does not lead to the strongest bond, but it is the highest flow values that provide the NHL2 and NHL3.5 mortars with the strongest bond and, in most instances, the highest water retention.