This paper deals with several concrete properties and to what extent they are influenced by slag and limestone filler, either one or both of them are included. Concrete was designed for low paste content, this is, a water reducing admixture (WR) was used to limit mixing water content. The results are compared with concrete made with commercial composite cement, blended during milling. Concrete was tested for compressive strength, sorptivity, resistivity, and water penetration under pressure. The volume of paste in all concrete mixes was the same.

Results showed the effect of slag on concrete transport properties. The effect of limestone filler was minimal either admixed solely or in conjunction with slag. On the other hand, blended cement appeared to be less effective on improving concrete transport properties. Compressive strength was less affected than transport properties by slag inclusion.

This investigation is on alternative cementitious materials of low cost, energy and environmental emissions. Portland cement (PC) was replaced by different types of calcium sulphate (hemihydrate HH, or anhydrite AN), fly ash (PFA) and cupola slag (CS) from an iron foundry. Pastes of blends of (HH or AN) – CS – PC and (HH or AN) – PFA – PC were characterized. The compositions varied within the ranges of 0 – 35% PC, 15 – 80% HH or AN, 10 – 80% CS and 10 – 80% PFA. The water/solids ratio was kept at 0.45 for HH blends and 0.37 for those of AN. The pastes were cured in dry and for some time under water. Selected blends of CS were repeated with blast furnace slag (BFS) for comparison. CS showed better results over PFA and less than BFS, perhaps as derived from its chemical composition, phase configuration and physical characteristics. These and other results of microstructural characterization will be discussed. This work is part of a broader research on the development of alternative environment friendly hydraulic composite cements of Portland cement highly replaced by calcium sulphate and industrial byproducts.

This research includes results on the corrosion performance of reinforcing steel in cement-based mortar (pH ~ 13) when cactus (Opuntia Ficus Indica –Nopal) slime was used as an addition. The cactus slime addition was mixed at different concentrations by mixing water mass (0%, 1.5%, 4%, 8%, 42%, and 95%). Half-cell potentials and LPR measurements were performed at different time periods to characterize the possible corrosion inhibiting effect of the cactus additions tested. Results showed good corrosion inhibiting effect of Nopal slime on reinforcing steel, in all tested solutions, when chloride ions were present. The addition of such cactus led to an apparent formation of a denser and more packed oxide/hydroxide surface layer on the steel surface that decreased corrosion activity. This oxide/hydroxide layer growth was confirmed from microscopic evaluation of the metal surface layer performed at the end of the research program. The preliminary findings suggest that adding Nopal slime in concentrations between 4% and 8%, by water mass, might be suitable for durability enhancing applications in cement-based mortar.

Silica fume is a very important supplementary cementitious binder in High-Performance and Ultra High-Performance Concretes. Through its pozzolanic reaction the silica fume densifies the concrete micro-structure, in particular it strengthens the paste-aggregate interfacial transition zone. In the present paper different aspects of the pozzolanic reaction of silica fume are investigated. These include chemical shrinkage, isothermal heat development and strength development. Key data for these are given and compared with theoretical calculations, and based on presented measurements the energy of activation of the pozzolanic reaction of silica fume is estimated. The results show that the pozzolanic reaction of silica fume has notable differences from Portland cement hydration.

The paper attempts to present a panoramic view of the water cement ratio strength relations adopted by a few national bodies and look at the appropriateness of them while keeping in mind the enormous number of variables that could influence them. These relations are also compared with a couple of databases reported to assess the efficacy of each of these in ensuring a reasonable prediction capability. This in a way will pave the way for an effective use of the cement in concrete leading to significant optimization of the concrete composite.

Optimal use of superabsorbent polymers (SAP) in cement-based materials relies on knowledge on how SAP absorbency is influenced by different physical and chemical parameters. These parameters include salt concentration in the pore fluid, temperature of the system and SAP particle size. The present work shows experimental results on this and presents a new technique to measure the swelling of SAP particles. This new technique is compared with existing techniques that have been recently proposed for the measurement of pore fluid absorption by superabsorbent polymers. It is seen that the concentration of Na+, K+, Ca2+, OH-, and SO2-, in the exposure liquid influences the maximum absorption of SAP. Even very low concentrations of these may reduce the absorption to a third of the value measured in pure water at room temperature. Additionally, the influence of the SAP absorption on the ionic composition of the exposure liquid is investigated with atomic absorption spectroscopy. The paper provides the reader with knowledge about the absorption capacity of SAP in a cementitious environment, and how the absorption process may influence the cement pore fluid.

Natural pozzolans are supplementary cementitious materials (SCMs) that may be used to improve the properties of mortar and concrete, through the formation of additional hydration products by pozzolanic action. Water reducers (WR) play a main role in high performance concrete in terms of durability, strength and surface finishing. A first optimization of constituent proportions in paste and/or mortar is convenient to assess the compatibility between the WR and the cementitious materials. The compatibility between cement and WR may be affected by SCMs, as they can also interact with the molecules of the admixture. However, the practical implication may be variable. This paper deals with the influence of different types and dosages of WRs in mortars made with pozzolanic Portland cement. Both medium and high ranges WRs have been used. Mortar fluidity has been tested by the spread and the slump tests. Results show different fluidizing capacities of WRs, among which polycarboxylate-based WR was the most compatible with the pozzolanic cement.

Self-compacting concretes have been of topical interest due to the ease of adoption and the significant savings in compaction efforts particularly at the congested reinforcement locations, in spite of the leak-proof forms required. However, many of the aspects regarding their production with different powder or pozzolanic additions and their corresponding mechanical strength characteristics are not yet fully understood. This paper deals exclusively with the compressive strength characteristics of these concretes incorporating limestone powder as a mineral admixture through the water cement ratio to strength results of concretes reported in literature. The basic idea is to get an idea of the SCCs at the lowest and the highest possible amounts of the limestone powder in it.

The damage that the products of microorganism metabolism, in particular biogenic sulfuric acid, do to hardened concrete is known as concrete biodeterioration. These microorganisms, Acidithiobacillus thiooxidans, Acidithiobacillus ferrooxidans and sulfate-reducing bacteria (SRB) are ubiquitous in the environment and they produce either hydrogen sulfide or sulfuric acid that can dissolve and disintegrate the concrete matrix. Their activity plays a very important function in the whole spectrum of degradation processes such as corrosion of reinforced metals and concrete.

In Canada and in the northern part of the United States, concrete structure failures from concrete biodeterioration are less common than in the southern part of the United States and in Mexico, nevertheless, it is a serious and expensive problem in hydraulic structures and sewage collection systems, which rapidly deteriorate. Also, leaking sewage systems result in the loss of groundwater resources particularly important in this arid region. Almost every city in the Mexican-American border region, who’s combined population is more than 15 million people, faces this problem. The U.S. cities have made some provision to face these concrete structure problems, but the Mexican cities have made less effort. Additives and admixtures are used to improve the properties of the concrete; nonetheless, we have exposed here the importance of the factual composition of the Portland cement and concrete to mitigate concrete biodeterioration in the hydraulic structures and sewage collection systems.

A carbonate form of Mg-Al-hydrotalcite and its p-aminobenzoate (pAB) modified derivative (i.e.,Mg(2)Al-pAB) were synthesized and characterized by means of XRD and FT-IR. The anticorrosion behavior was evaluated based on open circuit potential (OCP) of carbon steel in simulated concrete pore solution and chloride-exchange experiments. The preliminary results shown in this study demonstrated that ion-exchange indeed occurred between chlorides and the intercalated pAB anions in Mg(2)Al-pAB structure, thereby reducing the free chloride concentration in simulated concrete pore solution. The simultaneously released inhibitive pAB anions were found to exhibit the envisaged inhibiting effect and caused corrosion initiation of the steel shifting to a higher chloride concentration than without the modified hydrotalcites.

Important pore structure parameters related to mechanical properties and durability of cement-based materials can be determined by techniques such as scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and low temperature calorimetry (LTC). The methods provide information on porosity characteristics as pore volume, pore thresholds and/or pore size distribution in different size ranges and do therefore to a large extent supplement each other. Pastes of w/b=0.4 with 0%, 40% or 70% slag by volume were cured saturated at 20ºC for up to two years. The porosity was characterized by LTC, MIP, and SEM. Higher volume of pores was obtained by MIP compared to results obtained using LTC and SEM. Measured porosity was correlated with predicted porosity using information on the density and degree of hydration of the cement and slag. Porosity estimation showed best agreement with the porosity data measured by MIP. The use of slag showed the same trend for all tests: a higher total volume of pores, but a lower threshold pore size when compared with Portland cement paste. The findings illustrate the importance of measuring not only pore volume but also threshold pore sizes when characterizing porosity of cement-based materials with different binder compositions.

Sulfate attack on concrete has been studied worldwide for more than 60 years. However, the mechanisms of attack are still not entirely understood, and deterioration of concrete from sulfates still occurs. The source of the sulfates may be either external or internal. External sources are the naturally occurring sulfates in the environment or those sulfates that are the product of industrial processes or various human activities (e.g. fertilizers often release sulfates into the soil and groundwater). Internal sources of sulfates may include the sulfates introduced in the cements from which concrete is made. The purpose of this study is to find out the amount of sulfates that concrete can withstand in the water. Standards tests have been developed to evaluate the resistance of concretes to sulfate attack. Some, but not all of these tests, take into account the mechanisms of sulfate attack so far discovered in research work. The tests range from those that monitor changes in the strength of concrete specimens after set periods of immersion in known compositions sulfate solutions, to those that use x- ray diffraction to examine concrete specimens for expansive products (e.g. ettringite and thaumasite) that have resulted from sulfate attack.

Self-curing, or internal curing (IC), technology has been developed to counteract self-desiccation and autogenous shrinkage of high-strength/high-performance concrete (HSC/HPC), which is considered the "Achilles’ hill" of HSC/HPC [1]. According to ACI [2], IC refers to the process by which the hydration of cement continues because of the availability of internal water that is not part of the mixing water; while the internal water is made available by the pore system in structural lightweight aggregate (LWA) that absorbs and releases water. Recently ACI defined internal curing as “supplying water throughout a freshly placed cementitious mixture using reservoirs, via pre-wetted lightweight aggregates, that readily release water as needed for hydration or to replace moisture lost through evaporation or self-desiccation” [3]. Both definitions address the use of pre-wetted LWA as a self-curing (or internal curing) agent.

According to the definition of the RILEM Technical Committee TC-196 [4], IC implies introduction to the concrete mixture a component, which serves as a curing agent. This agent can be either a normal aggregate introduced into the concrete mixture in water-saturated state or a new component (for example, an additive or special aggregate). Similarly to the division accepted in external curing, RILEM TC-196 distinguishes between two categories of internal curing: (a) internal water curing (sometimes called “water entrainment”), when the curing agent performs as a water reservoir, which gradually releases water, and (b) internal sealing, when the curing agent is intended to delay/prevent loss of water from the hardening concrete. Although water-saturated porous aggregate is still the most popular material among IC agents, super-absorbent polymers (SAP), ceramic waste, recycled aggregate and wood-derived products show promising properties. In view of this, self-curing covers not only use of pre-wetted LWA, but also other methods of curing: water curing by means of variety of curing agents introduced in the concrete mix, and also the methods based on internal sealing.

The recent achievements in methods and materials for self-curing are reviewed, and the future trends in development of self-curing concrete are discussed.

A bacteria-based healing agent for concrete is currently under development in the Microlab of TU Delft. The agent consists of organic mineral precursor compound and bacteria in a protective reservoir. Cracks in the concrete matrix may be sealed and blocked by calcium carbonate based crystals, formed by bacterial conversion of mineral precursor compound. Given the solubility of the agent components, healing agent material may be prematurely released during the wet mixing stage, potentially influencing cement hydration and functionality of other concrete additions. Several materials have been selected as potential mineral precursor compound, being organic salts and a carbohydrate. Tests on standard mortar specimens show that strength development is not compromised when calcium lactate is added to the standard mixture. Calcium lactate was added to the mortar mixture either pure or in combination with a superplasticizer, either based on sulfonated naphthalene or modified polycarboxylate ether, to determine possible interferential effects.

Like broken bones are able to heal themselves, it would be desirable that damaged concrete may be repaired autonomously as high costs are related to the repair. Actually, concrete already has some self-healing properties; when cracks appear, water enters and reacts with unhydrated cement grains which results in crack healing. However, only small cracks can be healed in this way. Therefore, we want to improve the self-healing efficiency by adapting the concrete matrix. By introducing high amounts of fibers several small cracks appear instead of one large crack. Combination with superabsorbent polymers, also called hydrogels, provides immediate crack sealing. Another methodology is to embed encapsulated polymeric agents in the matrix. When cracks appear, the capsules break and the agent is released. Upon contact of both components, they react and the crack is healed. This technique is also combined with CaCO3 precipitation of bacteria. In that case, not only polymers but also bacteria and nutrients are encapsulated and released upon cracking. First the polymer reacts, later the bacteria start to convert the nutrients into CaCO3 crystals which make the polymer structure denser and thus seal the cracks completely. As crack healing by means of bacteria uses a repair material which is more compatible with concrete we also try to seal cracks by only using bacterial CaCO3. Therefore, bacteria are embedded inside aggregates. Upon cracking, bacteria are exposed to the air and when water enters the crack bacteria become active and fill the crack with CaCO3. From the first results it was noticed that due to autonomous crack healing, water permeability is reduced and regain in mechanical properties is obtained. This means that more durable concrete structures may be obtained by using the proposed self-healing techniques.

Using waste materials as aggregate for new concrete production is a growing tendency, because of several environmental problems. Recycled coarse aggregate (RCA) obtained from crushing waste concrete has lower density and greater absorption than natural aggregate, because of the higher porosity of the mortar attached to the RCA particles. Compressive strength level achieved in recycled concrete may be similar to that of conventional concrete. On the other hand, durable performance of recycled concrete is variable, and diverse evidence can be found in literature for different durability issues. In this paper, chloride ingress in conventional and recycled concrete, made with quartzite aggregate and blended Portland cement is evaluated when immersed in NaCl solution. Two strength levels (21 and 35 MPa) and two contents of RCA (25 and 75%), as substitute of natural quartzite aggregate, were considered. The chloride diffusion coefficient and the relationship between water-soluble chloride and bound chloride are analyzed.

Reactive magnesium oxide (magnesia, MgO) was produced by calcining magnesite at comparatively low temperature, less than 800 ℃C. The reactive MgO and fly ash were used as additives to cementitious binder. The reactive MgO-ordinary Portland cement-fly ash is referred to as MgO-OPC-FA cement in further. The hydration expansion effect of active magnesia on the properties of cementitious binder in different mixing ratio was investigated. It is known that the “dead burnt” MgO reacts with water very slowly, which causes the expansion after the solidification of cement. Therefore, the MgO content in ordinary cement is commonly restricted to less than 5%. Effects of reactive MgO on the expansion properties of the cementitious binders were studied. Hydrated products of reactive MgO cements were investigated by X-ray diffraction (XRD) and Scanning electron microscope (SEM) analysis. The MgO-OPC-FA cement was sound, although the content of reactive MgO in cement was about 8 wt. %. Reactive MgO was hydrated at early age in 24 hours, thus causing rapid expansion. Mg(OH)2appeared on initial stage of cement hydration for active magnesia. The hydration rate of active magnesia was not equal to that of the dead burnt magnesia. The hydration of reactive MgO has a negative effect on the mechanical properties of reactive MgO-ordinary Portland cement-fly ash system, in spite of the inhibitive effect of the expansion of MgO hydration produced by fly ash. Our results shed light on the potential utilization of reactive MgO in the manufacturing of cementitious binders.

The information about concentrations of natural radionuclides in concrete mix and mineral raw materials used for concrete manufacture, supplementary cementitious materials (SCM) including, can be helpful for determination of concrete composition. The paper deals with the novel approach to determine concrete mix composition – using gamma-ray spectrometry.

In order to determine concrete composition, the content of naturally occurring radioactive materials (NORM) was determined in cement, FA and aggregates. Concrete compositions of both fresh and hardened mixes were determined by solving an over-determined system of four algebraic equations. The over-determined system consists of three equations, which represent activity concentrations of 226Ra, 232Th and 40K in concrete mix as a function of activity concentrations of the same radionuclides in cement, fly ash and aggregates, and the fourth conditional equation representing a sum of volumetric concentrations of cement, fly ash, aggregates and water in concrete mix as 100%. An over-determined system of linear equations was solved by the method of Lagrange multipliers, which provides a strategy for finding the maxima and minima of a function subject to constraints.

Gamma spectrometry was found very sensitive to the presence of FA in both fresh and hardened concrete, while 232Th activity concentration - well correlated with the FA content in the mixes. On the contrary, accurate determination of the rest of concrete composition was difficult.

A wide variety of materials are currently used as supplementary cementitious materials (SCMs) for concrete, including natural materials and byproducts from various industries. Historically, natural SCMs, mostly derived from volcanic deposits, were common in concrete. In recent years, the dominant SCMs have been industrial by-products such as fly ash, ground granulated blast furnace slag (GGBFS), and silica fume. There is currently a resurgence of research into historic and natural SCMs, as well as other alternative SCMs for many reasons. The primary benefits of SCM use in improvement of long-term mechanical performance, durability, and sustainability are widely accepted, so local demand for these materials can exceed supply. This paper describes some of the SCMs that are attracting attention in the global research community and the properties and characteristics of these materials that affect their performance. Special attention is paid to the importance and demands of material characterization. Many SCMs do not necessarily lend themselves to characterization methods used in standardized test methods, which sometimes fail to describe the properties that are most important in predicting reactivity.

Red mud is a solid waste residue from the caustic soda leaching of bauxite ores to produce alumina by the Bayer process. Red mud contains large quantity of alkali and aluminosilicate, so it is potentially available to prepare inorganic polymeric materials by geopolymerisation process. However, the activity or dissolubility of the aluminosilicate phases in red mud is significantly poor, which constraints the geopolymerisation process. Therefore, some pretreatment process for red mud is necessary to improve the adhesive property and dissolubility of Bayer red mud. In this study, mineral phase transformation and dissolubility of a typical red mud sample were studied under different thermal treatment processes. The thermal behavior of the red mud was studied by TG-DTA. The crystalline phases of the samples calcined at 200-1000 °C for different hours were determined by XRD, and the dissolubility was determined by alkaline leaching test. The TG-DTA pattern shows no obvious endothermic or exothermic peaks, and the weight loss increases continuously as the temperature rises, which indicates that the crystalline phases transform continuously as the temperature rises, consistent with the XRD results. As the calcination temperature rises from 200 to 800 °C, several kinds of crystalline phase in original red mud, including gibbsite, katoite, muscovite, natrodavyne disappeared in succession, accompanied with the formation of nepheline, gehlenite, sodium aluminum silicate, and some amorphous aluminosilicate. The calcined products are more likely to dissolve. But when it rises over than 800 °C, the content of gehlenite increases, and the phase of which is stable. As the calcination temperature rises from 200 to 1000 °C, the dissolubility of aluminosilicate in the red mud under high alkaline conditions increases firstly and then decreases after over 800 °C. Therefore, the optimum temperature of thermal treatment for red mud is about 800 °C. This study could contribute to the following preparation of geopolymeric material made from red mud, especially the pretreatment process of red mud.