Compressive strength and durability properties of ceramic wastes based concrete

This paper presents an experimental study on the properties and on the durability of concrete containing ceramic wastes. Several concrete mixes possessing a target mean compressive strength of 30 MPa were prepared with 20% cement replacement by ceramic powder (W/B = 0.6). A concrete mix with ceramic sand and granite aggregates were also prepared as well as a concrete mix with natural sand and coarse ceramic aggregates (W/B = 0.5). The mechanical and durability performance of ceramic waste based concrete are assessed by means of mechanical tests, water performance, permeability, chloride diffusion and also accelerated aging tests. Results show that concrete with partial cement replacement by ceramic powder although it has minor strength loss possess increase durability performance. Results also shows that concrete mixtures with ceramic aggregates perform better than the control concrete mixtures concerning compressive strength, capillarity water absorption, oxygen permeability and chloride diffusion. The replacement of cement and aggregates in concrete by ceramic wastes will have major environmental benefits.     

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.     

Mix design method for self compacting metakaolin concrete with different properties of coarse aggregate

This study deals with a proposed mix design method for SCC utilizing different properties of coarse aggregate. The work was conducted in three phases, i.e. paste, mortar and concrete to facilitate the mix design process. Initial investigation on cement paste determined the basis for water cement ratio and superplasticizer dosage for the concrete. For the study on mortar, metakaolin (MK) as pozzolan was used at replacement levels of 5%, 10%, 15%, and 20% by weight of cement. Self compactability of mortars was obtained by adding suitable materials such as mineral admixtures and superplasticizer which provided a sufficient balance between flowability and viscosity of the mix. The optimum MK replacement level for cement was 10% from the viewpoint of workability and strength. Flowability of mortar decreased with the use of metakaolin. Moreover, strength of mortar increased when the optimum replacement level of pozzolan was used. Different fresh concrete tests were adopted. The results obtained for fresh concrete properties showed that flowability of concrete increased with increase flowability of mortar. The mixes which contained coarse aggregate with lower volume, small size, and continuous grading affected positively the fresh properties of SCC. Finally, the mix design method used was successful in producing SCC with different coarse aggregate properties.     

Thixotropy and structural breakdown properties of self consolidating concrete containing various supplementary cementitious materials

In this study, thixotropy and structural breakdown of 57 self-consolidating concrete (SCC) mixtures containing various supplementary cementitious materials (SCM) were investigated by different approaches. The effects of SCM type and content on high range water reducer demand and plastic viscosity were also studied. For these purposes, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends in three water/binder (w/b) ratios. Results showed that except BFS, use of SCM in SCC mixtures increased thixotropy values in comparison with the mixtures containing only portland cement (PC). Good correlations were established between structural breakdown area and drop in apparent viscosity values for all w/b ratios. The different methods used to evaluate the thixotropy and structural breakdown got more consistent with each other as w/b decreased.     

Effect of admixtures on the setting times of high-strength concrete

The effect of silica fume (SF), metakaolin (MK), fly ash (FA) and ground granulated blast-furnace slag (GGBS) on the setting times of high-strength concrete has been investigated using the penetration resistance method (ASTM C 403). In addition, the effect of a shrinkage-reducing admixture (SRA) on the setting times of normal and high-strength concrete was also studied. The setting times of the high-strength concrete were generally retarded when the mineral admixtures replaced part of the cement. While the SRA was found to have negligible effect on the setting times of normal strength concrete, it exhibited a rather significant retarding effect when used in combination with superplasticiser in high-strength concrete. The inclusion of GGBS at replacement levels of 40% and greater resulted in significant retardation in setting times. In general, as replacement levels of the mineral admixtures were increased, there was greater retardation in setting times. However, for the concrete containing MK, this was only observed up to a replacement level of 10%.     

Comparative study on strength,sorptivity, and chloride ingress characteristics of air-cured and water-cured concretes modified with metakaolin

This paper reports an investigation in which the performance of plain and metakaolin (MK)-modified concretes were studied under two different curing regimes. The purpose of this study is to evaluate the effectiveness of MK in enhancing the strength and permeation properties of concrete. MK was used to replace 0–20% of Portland cement by weight in concrete with two water-binder (w/b) ratios of 0.35 and 0.55. The change in compressive strength, sorptivity, and chloride ingress with age at all cement replacement levels under both air and water curing are compared with those of the control concrete. The results indicated that the inclusion of MK greatly reduced sorptivity and chloride permeability of concrete in varying magnitudes, depending mainly on replacement level of MK, w/b ratio, curing condition, and chloride exposure period. It was found that under the inadequate or poor curing, MK-modified concretes suffered a more severe loss of compressive strength and permeability-related durability than the plain concretes.     

Effect of pozzolans on the performance of fiber-reinforced mortars

Randomly oriented short fibers have been shown to increase tensile strength and retard crack propagation of cement based materials such as fiber-reinforced mortars for diverse applications, especially in aggressive environments. In the case of reinforced concrete, it is very important to produce a “high quality” cover in order to prevent corrosion of the rebars. In order to obtain a high performance material the use of a pozzolan is advisable because low permeability is achieved. The objective of this research was to determine the effect of pozzolans such as silica fume (SF), fly ash (FA), and metakaolin (MK) on the properties of fiber-reinforced mortars. Different types of natural and synthetic fibers were used. A superplasticizer was used to keep the same workability as that of the control mortar. Results of the mechanical and durability properties of the fiber-reinforced mortars are reported. The results show that a loss of resistance due to embedding fibers in mortar is compensated for by the increase in strength caused by silica fume or metakaolin additions to the mortar. The addition of 15% of SF or MK produces an improvement of up to 20% and 68%, respectively, when compared with those mortars without addition. There is a significant decrease in the coefficient of capillary absorption and chloride penetration when a highly pozzolanic material is incorporated into the matrix. In general, these materials, especially SF and MK, improve the mechanical performance and the durability of fiber-reinforced materials, especially those reinforced with steel, glass or sisal fibers. The fly ash addition had a different performance, which could be attributed to its low degree of pozzolanicity.     

Effect of metakaolin on the near surface characteristics of concrete

Results on an investigation dealing with the effect of metakaolin (MK) on the near surface characteristics of concrete are presented in this paper. A control concrete having cement content 450 kg/m³ and w/c of 0.45 was designed. Cement was replaced with three percentages (5, 10, and 15%) of metakaolin weight. Tests were conducted for initial surface absorption, sorptivity, water absorption and compressive strength at the ages of 35, 56, and 84 days. Test results indicated that with the increase in MK content from 5 to 15%, there was a decrease in the initial surface absorption, decrease in the sorptivity till 10% metakaolin replacement. But at 15% MK replacement an increase in sorptivity was observed. All mixtures showed low water absorption characteristic i.e. less than 10%. Compressive strength shared an inverse relation with sorptivity. Higher MK replacements of 15% are not helpful in improving inner core durability, even though it helps in improving surface durability characteristics.     

A model predicting carbonation depth of concrete containing silica fume

Silica fume (SF) has been used since long as a mineral admixture to improve durability and produce high strength and high performance concrete. Due to the pozzolanic reaction between calcium hydroxide and silica fume, compared with ordinary Portland cement, the carbonation of concrete containing silica fume is much more complex. In this paper, based on a multi-component concept, a numerical model is built which can predict the carbonation of concrete containing silica fume. The proposed model starts with the mix proportions of concrete and considers both Portland cement hydration reaction and pozzolanic reaction. The amount of hydration products which are susceptible to carbonate, such as calcium hydroxide (CH) and calcium silicate hydrate (CSH), as well as porosity can be obtained as associated results of the proposed model during the hydration period. The influence of water-binder ratio and silica fume content on carbonation is considered. The predicted results agree well with experimental results.     

Use of ultrafine rice husk ash with high-carbon content as pozzolan in high performance concrete

Rice husk ash (RHA) has been generated in large quantities in rice producing countries. This by-product can contain non-crystalline silica and thus has a high potential to be used as cement replacement in mortar and concrete. However, as the RHA produced by uncontrolled burning conditions usually contains high-carbon content in its composition, the pozzolanic activity of the ash and the rheology of mortar or concrete can be adversely affected. In this paper the influence of different grinding times in a vibratory mill, operating in dry open-circuit, on the particle size distribution, BET specific surface area and pozzolanic activity of the RHA is studied, in order to improve RHA’s performance. In addition, four high-performance concretes were produced with 0%, 10%, 15%, and 20% of the cement (by mass) replaced by ultrafine RHA. For these mixtures, rheological, mechanical and durability tests were performed. For all levels of cement replacement, especially for the 20%, the ultra-fine RHA concretes achieved superior performance in the mechanical and durability tests compared with the reference mixture. The workability of the concrete, however, was reduced with the increase of cement replacement by RHA.     

Strength,sorption and abrasion characteristics of concrete using ferrochrome ash (FCA) and lime as partial replacement of cement

This paper presents the results of experimental investigations and microstructure study carried out to evaluate the possibility of utilization of ferrochrome ash (FCA), a waste product from ferroalloys industries for partial replacement of cement in concrete preparation. FCA is used in four different substitution rates such as 10, 20, 30 and 40% along with 7% lime. Various strength and durability tests were conducted to understand the effects of FCA and lime on performance of concrete. Test results revealed that replacement of cement by FCA in various % with 7% lime enhanced the 28 days compressive strength 1.5–13.5%, flexural strength 4.5–9%, bond strength 15–29%, abrasion resistance 10–23% and reduced the sorptivity 25–43%. The concrete containing 40% FCA and 7% lime, replacing 47% of ordinary Portland cement (OPC) in total, exhibited strength of normal concrete or even more at all ages. XRD and petrography studies confirmed the results of mechanical and durability properties.     

Compressive strength and chloride resistance of self-compacting concrete containing high level fly ash and silica fume

The influence of high-calcium fly ash and silica fume as a binary and ternary blended cement on compressive strength and chloride resistance of self-compacting concrete (SCC) were investigated in this study. High-calcium fly ash (40–70%) and silica fume (0–10%) were used to replace part of cement at 50, 60 and 70 wt.%. Compressive strength, density, volume of permeable pore space (voids) and water absorption of SCC were investigated. The total charge passed in coulombs was assessed in order to determine chloride resistance of SCC. The results show that binary blended cement with high level fly ash generally reduced the compressive strength of SCC at all test ages (3, 7, 28 and 90 days). However, ternary blended cement with fly ash and silica fume gained higher compressive strength after 7 days when compared to binary blended fly ash cement at the same replacement level. The compressive strength more than 60 MPa (high strength concrete) can be obtained when using high-calcium fly ash and silica fume as ternary blended cement. Fly ash decreased the charge passed of SCC and tends to decrease with increasing fly ash content, although the volume of permeable pore space (voids) and water absorption of SCC were increased. In addition when compared to binary blended cement at the same replacement level, the charge passed of SCC that containing ternary blended cement was lower than binary blended cement with fly ash only. This indicated that fly ash and silica fume can improve chloride resistance of SCC at high volume content of Portland cement replacement.     

Transport and mechanical properties of self consolidating concrete with high volume fly ash

This paper presents the transport and mechanical properties of self consolidating concrete that contain high percentages of low-lime and high-lime fly ash (FA). Self consolidating concretes (SCC) containing five different contents of high-lime FA and low-lime FA as a replacement of cement (30, 40, 50, 60 and 70 by weight of total cementitious material) are examined. For comparison, a control SCC mixture without any FA was also produced. The fresh properties of the SCCs were observed through, slump flow time and diameter, V-funnel flow time, L-box height ratio, and segregation ratio. The hardened properties included the compressive strength, split tensile strength, drying shrinkage and transport properties (absorption, sorptivity and rapid chloride permeability tests) up to 365 days. Test results confirm that it is possible to produce SCC with a 70% of cement replacement by both types of FA. The use of high volumes of FA in SCC not only improved the workability and transport properties but also made it possible to produce concretes between 33 and 40 MPa compressive strength at 28 days, which exceeds the nominal compressive strength for normal concrete (30 MPa).     

The fluid transport properties of HCWA–DSF hybrid supplementary binder mortar

It has been demonstrated in several past studies that high calcium wood ash (HCWA) can be effectively used in combination with densified silica fume (DSF) as supplementary binder material to enhance the mechanical performance of concrete. The experimental investigation was conducted to study the effect of the inclusion of HCWA and DSF on the durability properties of high strength cement mortar produced. A total of twelve different mix designs of mortar were fabricated with the use of HCWA at various cement replacement levels of 0–20% in combination with 7.5% densified silica fume (DSF) and subjected to various durability tests. The durability assessments performed include tests on water absorption, air permeability, porosity and degree of carbonation. A significantly lower degree of water absorption, porosity and carbonation was observed for cement mortars with HCWA contents of 2–8% used in combination with 7.5% DSF by weight of binder as compared to an equivalent pure cement mortar.     

Durability aspect of concretes composed of cold bonded and sintered fly ash lightweight aggregates

This study reports the finding of an experimental study carried out on the durability related properties of the lightweight concretes (LWCs) including either cold bonded (CB) or sintered (S) fly ash aggregates. CB aggregate was produced with cold bonding pelletization of class F fly ash (FA) and Portland cement (PC) while S aggregate was produced by sintering the fresh aggregate pellets manufactured from FA and bentonite (BN). Two concrete series with water-to-binder (w/b) ratios of 0.35 and 0.55 were designed. Moreover, silica fume (SF) with 10% replacement level was also utilized for the purpose of comparing the performances of LWCs with and without ultrafine SF. The durability properties of concretes composed of CB and S aggregates were evaluated in terms of water sorptivity, rapid chloride ion permeability, gas permeability, and accelerated corrosion testing after 28 days of water curing period. The compressive strength test was also applied to observe the strength level at the same age. The results revealed that S aggregate containing LWCs had relatively better performance than LWCs with CB aggregates. Moreover, the incorporation of SF provided further enhancement in permeability and corrosion resistance of the concretes.     

Effect of metakaolin on creep and shrinkage of concrete

The effect of metakaolin (MK) on the creep and shrinkage of concrete mixes containing 0%, 5%, 10%, and 15% MK has been investigated. The results showed that the early age autogenous shrinkage measured from the time of initial set of the concrete was reduced with the inclusion of MK, but the long-term autogenous shrinkage measured from the age of 24 h was increased. At 5% replacement level, the effect of MK was to increase the total autogenous shrinkage considered from the time of initial set. While at replacement levels of 10% and 15%, it reduced the total autogenous shrinkage. The total shrinkage (autogenous plus drying shrinkage) measured from 24 h was reduced by the use of MK, while drying shrinkage was significantly less for the MK concretes than for the control concrete. The total creep, basic creep as well as drying creep were significantly reduced particularly at higher MK replacement levels. Compared with estimated values by the CEB 90 model, total creep of all concretes was overestimated, especially in the mixes containing the higher levels of MK. For basic creep, estimates for low levels of MK were acceptable but, for the higher levels, creep was overestimated.     

Effect of utilizing unground and ground normal and black rice husk ash on the mechanical and durability properties of high-strength concrete

The aim of the present study is to investigate the effects of utilizing different processings of normal rice husk ash (RHA) and black rice husk ash (BRHA) on the mechanical and durability properties of high-strength concrete (HSC). Mechanical and durability properties of HSC were evaluated on concrete mixes containing unground BRHA and RHA and ground BRHA and RHA, their average particles sizes being 165, 85, 67 and 24 µm, respectively. The replacement of ordinary Portland cement with the ashes was adopted at 20%. The results showed that incorporating any form of RHA and BRHA in HSC reduced the slump value. The surface areas of RHA and BRHA, not their carbon content, determined the dosage of superplasticizer needed to achieve a targeted slump value. Concrete with unground and ground RHA incorporated exhibited 30% higher compressive strength while unground BRHA produced 30% lower compressive strength than that of the control concrete. Incorporating unground and ground RHA showed a synergy between filler and pozzolanic effect and had insignificant difference in mechanical and durability properties of the concretes. Meanwhile, incorporating ground BRHA showed a dominant filler effect in the concrete. Overall, the improvement of splitting tensile strength and modulus of elasticity of both RHA and GBRHA concrete showed a similar trend to that of the compressive strength of RHA concrete. The durability of concretes with unground and ground RHA and ground BRHA incorporated showed better performance than that of the control concrete. The material with 20% ground BRHA as partial cement replacement in HSC of Grade 50 could be used without any reduction in the mechanical and durability properties. Use of unground BRHA is not recommended because it did not improve these properties.     

Effect of reinforcement on plastic shrinkage and settlement of self-consolidating concrete as repair material

The experimental investigation on plastic shrinkage and plastic settlement for different self-consolidating concrete (SCC) mixtures as repairing materials is presented. The concrete mixtures were placed on the surface of the concrete substrate slabs at different restraint degrees. Four different types of repairing materials such as plain SCC, SCC with silica fume (SF), SCC with latex and SF, and SCC with latex, SF and fiber were evaluated. The slabs included both reinforcement and without reinforcing bars. The tests involved measurement of concrete bleeding and evaporation rates, steel bar strains and crack characteristics. The results indicated that bleeding rate is not the only controlling factor, but restraint condition, configuration of steel bars and the concrete strain capacity are also affect plastic shrinkage and settlement behaviors significantly. Latex and fiber were found to be effective in reduction of cracks and concrete strains. Cracks did not develop on the surface of concrete containing latex and fiber. The results showed that if a slab is reinforced by one single bar (in each direction of the slab), at relatively large diameter as used in this study, it would not improve the plastic shrinkage behavior, although it causes plastic settlement cracking.     

Influence of key cement chemical parameters on the properties of metakaolin blended cements

The use of metakaolin (MK) as a mineral admixture for cement and concrete is a well-documented practice. The properties of cement pastes and mortars containing MK have been investigated as a function of key cement chemical parameters recognized as potential activators of the MK. Rheological behavior, initial setting time and compressive strength development have been compared by varying the total sulfate content, the nature of the added calcium sulfate and the free lime content (in the form of portlandite) in the cement. The results obtained indicate that it exists a compromise for the ratio performance/consistency in term of sulfate content and nature. Concurrently, a small addition of portlandite improves the consistency of the properties investigated.