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In this paper, perlite mining and rice production by-products, namely run-of-mine perlite and rice husk ash, are used as fine aggregates in combination with pumice and calcareous aggregates to produce lightweight concrete. Their use is evaluated mainly in terms of the durability of the concrete, by comparing four optimized lightweight concrete mixtures of similar density and strength with a reference one of normal weight. The sorptivity due to capillary sorption, open porosity, chloride migration, penetration resistance, and freeze and thaw response were studied to evaluate the durability of the lightweight concrete. According to the experimental results, the examined mixtures developed an adequate strength in order to be classified into strength classes greater than LC25/28 and, therefore, be used in structural applications. The durability of the mixtures was also sufficient, especially as far as the chlorides’ penetration resistance is concerned, which was found to be up to 39% lower compared to the reference mixture. The sorptivity and open porosity of the LWC mixtures increased due to the porous nature of the lightweight aggregates, and the mixtures were also found to be susceptible to freeze and thaw cycles. Exceptionally, the lightweight concrete mixtures comprising pumice and perlite exhibited a lower sorptivity and resistance to chloride penetration than the standard concrete and a promising tolerance to freezing and thawing. Thus, the optimized combination of pumice and perlite is a sustainable recommendation for structural lightweight concrete production and use, promoting the wider exploitation of natural aggregates with an acceptable compromise on strength and durability.

Open Innovation has great significance and so far several definitions have been proposed, the most widely accepted definition referring to the correlation of Open Innovation with research organizations. Helix models have been proposed to analyze how collaborations work among key stakeholders and research centers and they were found to have a prominent part in all their iterations. This work presents the challenges that research organizations face in terms of interaction with other organizations, their operations (resources, funding issues), and how they determine the research directions to be followed, and analyzes how the adoption of Open Innovation practices can tackle these challenges and the effects it has. The Open Innovation practices of outsourcing and co-creation are mentioned, with the latter needing to be further developed and elaborated. We propose a novel process, called Research Loop, which aims and succeeds to provide Open Innovation for research organizations. It achieves to involve several different organizations, identify existing research gaps, and produce new knowledge. The proposed process includes the various advantages of applying Open Innovation to the analyzed research centers.

Upon presenting the particularities of the Arabian Peninsula on the durability of reinforced concrete structures, the procedure and outcomes of a durability analysis using a physicochemical deterministic service life estimation tool on a major infrastructure project of the region, that the authors were invited to perform, are presented. The results show that the initially performed stochastic durability analysis was validated, and further enhancements were proposed. It is argued that a verified physicochemical deterministic approach can produce accurate results under the highly aggressive environment of the Arabian Peninsula, which if necessary, can be further enriched using calibrated reduction (safety) factors.

In the absence of a carbonation model for soil cement, this research aims to assess the compatibility and applicability of an analytical model initially developed for concrete. Carbonation can be observed in any pavement layer which includes cement or lime. For instance, carbonation damages the cement-modified crushed rocks as a typical material for base course layer due to poor curing of material or cracking of asphalt. Experimental laboratory tests are utilised here in accelerated carbonation conditions to evaluate the analytical model. Cylindrical specimens are subjected to one-dimensional carbonation condition. Weight and ratio of constituents of mixes, as well as environmental factors, such as CO 2 concentration and relative humidity are recorded for analytical estimation of failure progresses. Nanosilica is also introduced in mixes to explore its effects during carbonation reactions. Results show linear correlations between experimental records and analytical model calculations. Thus, it can be concluded that carbonation rate can be predicted in soil cement also. In addition, the inclusion of nanosilica has a positive influences by slowing of the carbonation progress.

In this paper, the effect of the addition of metakaolin on chloride-penetration resistance of concrete is investigated. Greek kaolin thermally treated at defined conditions and a commercial metakaolin were used. Eight mixture proportions were used to produce high performance concrete, where metakaolin replaced either cement or sand in percentages 10% or 20% by weight of the control cement content. The specimens were placed in a NaCl solution for 90 days and the concentration of total and free (unbound) chloride was determined. The chloride penetration was studied by means of a fundamental model taking into account diffusion and binding (adsorption & desorption) processes. The efficiency factors (k-values) for the studied metakaolins were determined. Both metakaolins present a considerable chloride-penetration resistance, depending on active silica and alumina contents, and their addition significantly decreases chloride penetration leading to improved concrete durability.

Utilization of biomass ash from agro-industrial by-products (containing large amounts of silica in amorphous form) in cement manufacturing and/or concrete production can be an alternative solution to the incorporation of the traditionally used supplementary cementing materials (SCMs). An evaluation of biomass ashes, identified in the literature, with varying SiO2 contents in terms of concrete strength and performance in chloride exposure is the focus of this study. Results indicate that these materials are effective on concrete strength development and extremely efficient in reducing the concrete permeability. The dependency of this behavior on the level of SiO2 of the ash content was examined in depth and was concluded that it is affected by the composition of other components of the biomass ash.

Research on ash from burning of rice husks (RHA) has already demonstrated that it is one of the most promising supplementary cementing materials (SCM), given its high specific surface and great amount of silica soluble in alkaline conditions. Indeed, RHA could be a product of added value if it wasn't for its limited availability and periodically high residual carbon content, factors inhibiting its wider use in building materials. Most of the published work has exploited the effectiveness of RHA of very high specific surface and reactive silica, without really investigating the effect of these factors with respect to mechanical and durability characteristics of the derived cement and concrete. This is of crucial importance since someone could falsely rate RHA of moderate fineness and chemical reactivity as potentially reject, constituting thus a significant portion of this by-product unutilised. Reactive silica and fineness effect was assessed in this study by examining two different RHAs, both in blended cement and concrete level. It was found out that RHA is a material extremely “sensitive” to fineness changes; the higher being the fineness the more positive is the effect of RHA inclusion in the mix. Not surprisingly, active silica holds a key role especially for later-age strength gain, indicating that pozzolanic effect takes over from the “physical” effect of the pozzolan as hydration evolves. Pozzolanic potential, strength development of mortars and concrete, efficiency factors (k-values) estimation and resistance against chloride penetration are part of the testing performed and reveal the importance of the binary action of RHA in producing competitive blended cement and concrete.

A significant step forward for a thorough durability design process of reinforced concrete structures is the development of software packages, based on predictive models, for the estimation of concrete strength and service life. Such an attempt, in full compliance with the European Standards for cement and concrete, is presented in this study. Upon defining the concrete mix design, the software calculates the main chemical and volumetric characteristics, as well as the compressive strength, of concrete. By taking into account the environmental conditions where the structure will be exposed, concrete service life is predicted, using fundamental mathematical models (based on reaction engineering principles) that simulate the reinforced concrete deterioration mechanisms leading to corrosion of the embedded reinforcement (caused by either carbonation or chloride ingress). A validation process of the yielded results is also presented, and the effectiveness of the simulation tool in designing for durability is illustrated. The goal of this study is to promote wider acceptance in achieving feasible and durable solutions to structural concrete design problems.

The need for a structured durability design process of reinforced concrete elements is strongly emphasized in the current study. Under such a framework, concrete service life estimation tools (SLTs) can be vital aids. Their utilization however is not an easy process and might lead to confusing results for the same element under the same harsh environment, as it is presented via a case study in this work. The reasons for such a behavior are explained and the next steps and research actions that have to be taken in establishing a widely accepted durability design process are discussed.

In contrast to common approach – that often involves extensive pre-grinding – the utilization potential of rice husk ash (RHA: by-product of rice industry) as a supplementary cementing material, in its untreated form was examined. This is to meet industry’s increasing awareness for lower embodied energy cement and concrete. Given the availability of current raw materials in cement manufacturing, what is needed is to be able to achieve an optimum approach, between sustainability and durability when designing concrete structures. Under this frame, as-produced RHAs (D50 of approx. 70 μm) were examined with respect to their inherent characteristics and their impact on the performance of cement-based mortars. Strength, hydration and durability properties were considered. Untreated RHA exhibits moderate pozzolanicity and a low efficiency factor of approximately 0.5–0.6. Its very high chemical reactivity (active silica ratio of approx. 90%) cannot be exploited since the lack of adequate specific surface slows down its engagement in hydration reactions. Taking into consideration their untreated nature, it can be supported that they exhibit an acceptable strength potential after 28 days, complying – even marginally – with the strength class (42.5) of the used cement. Durability results revealed that there is no need to pre-treat RHA in order to achieve equal or even better performance than mortar with plain cement in terms of sorptivity (50% increase for 15% RHA usage) and resistivity. Untreated RHA however fails – as most SCMs do – to improve carbonation resistance since for a 15% cement replacement, carbonation depth was almost doubled. Overall, results indicate that usage of untreated RHA in cement-based systems is an alternative to decrease their carbon profile, as long as cement replacement is kept relatively low (below 15%).

While recognizing the problem of reinforcement corrosion and premature structural deterioration of reinforced concrete (RC) structures as a combined effect of mechanical and environmental actions (carbonation, ingress of chlorides), emphasis is given on the effect of the latter, as most severe and unpredictable action. In this study, a simulation tool, based on proven predictive models utilizing principles of chemical and material engineering, for the estimation of concrete service life is applied on an existing reinforced concrete bridge (O resund Link) located in a chloride environment. After a brief introduction to the structure of the models used, emphasis is given on the physicochemical processes in concrete leading to chloride induced corrosion of the embedded reinforcement. By taking under consideration the concrete, structural and environmental properties of the bridge investigated, an accurate prediction of its service life is taking place. It was observed that the proposed, and already used, relationship of service lifetime- cover is almost identical with a mean line between the lines derived from the minimum and maximum critical values considered for corrosion initiation. Thus, an excellent agreement with the project specifications is observed despite the different ways used to approach the problem. Furthermore, different scenarios of concrete cover failure, in the case when a coating is utilized, and extreme deicing salts attack are also investigated.

In the current study the effects of chloride-induced corrosion, in terms of mechanical properties and pit depths, are evaluated on B500c steel bars embedded in concrete (embedded samples) and directly exposed (bare samples), immersed in a salt spray chamber. The results indicate that for the same level of mass loss, degradation of the “embedded” samples was found to be much more severe than that of the “bare samples”, in terms of losses in yield strength and uniform elongation. Analysis of the statistical significance of the pit depth and area values measured, based on a methodology developed using advanced imaging analysis, indicate that degradation of the steel bars embedded in concrete produced a more severe pitting corrosion in terms of depth of pitting, compared to the steel samples directly exposed to the same corrosive medium, for the same (on average) mass loss.

In all concrete constructions besides the common strength problems, in presence or not of seismic activity, serious problems from environmental attack may be presented which significantly decrease their durability and service lifetime. The most common case of construction deterioration is the corrosion of steel reinforcement. The initiation mechanisms leading to steel depassivation, such as concrete carbonation and chloride penetration, have been thoroughly studied and modeled in the past. However, for the corrosion propagation period still there are no acceptable models to simulate the corrosion rate and further to estimate precisely the time when the corrosion progress signals the end of the structure service life. In the present work, the main corrosion initiation mechanisms are shortly presented. Further, the propagation period and the main consequences on mechanical properties of steel and concrete are analyzed. The experimental results show that with increasing duration of exposure to a corrosive environment, the steel mass loss increases appreciably. This leads to a significant increase of the applied stress. In addition, a significant reduction of the tensile ductility of the material was observed. For laboratory salt spray exposure periods, some of the tensile properties of steel bars drop to values lying below the limits, which are set in the existing standards for using steels in reinforced concrete members. The experimental results from the accelerated corrosion tests on bare steel bars are in a good qualitative agreement with results from steel bars embedded in aged concrete.

Even though the use of pozzolanic and latent hydraulic materials (such as fly ash, slag and natural pozzolans) in the construction sector is nowadays a common practice, certain deficits associated with these materials have initiated research that aims to reduce the negative effects that they introduce into cementitious systems. With respect to fly ash, its relatively slow pozzolanic reactivity hinders its greater utilization; hence cost efficient methods of activation are on demand. In this work, cement systems containing the two typical types of Hellenic fly ashes (of high and moderate calcium content) were chemically activated by adding industrially produced quicklime. A first step in assessing the efficiency of the above procedure was based in monitoring the compressive strength development, lime depletion values and data derived from a selective dissolution procedure (based on a mixture of picric acid–methanol). Moreover, evolution of the fly ash reaction and the morphology of the formed hydration products were examined by means of scanning electron microscopy. Evidence included in this investigation reveal that quicklime presence accelerated the reaction rate of high-calcium fly ash, whereas in the case of lower-calcium fly ash, quicklime had a positive impact only during the very early stages of hydration and thereafter acted inhibitory with respect to its reactivity development.

For overcoming certain drawbacks characterizing both basic types of fly ashes (of high and low calcium content), different ash intermixtures consisting of two types of fly ashes were prepared. The principal idea lying beneath the effort presented herein is that beneficial assets of the one type of ash could compensate for the shortcomings of the other. Compressive strength development, pozzolanic activity potential and nature of hydration products of all ternary cements were closely monitored and presented in comparison to the respective properties of the initial binary blends. Moreover, efficiency factors were calculated for all new systems and were further used to validate previously reported expressions describing Binary Fly ash-Cement (BFC) systems. In accordance with previous works, ternary fly ash systems examined here outperformed the respective binary systems almost throughout the curing period. Synergy between the different types of fly ashes was considered the main reason for the excellent performance of the ternary mixtures. Results obtained indicate that previously developed analytical expressions, correlating active silica of SCMs and k-values, can be applied in the case of multicomponent ash systems as well.

Sustainable development of the building sector can be achieved by a significant incorporation of cementitious and pozzolanic by-products, such as fly ash and slag, as well as some natural pozzolanic materials (supplementary cementing materials--SCM). Millions of tons of SCM, especially in Greece, are dumped due to overproduction or non-conformity with the existing standards. In this work, various types of SCM produced in Greece are investigated for a potential use in concrete. Their behavior as regards strength and durability is approached by a practical efficiency factor (k-value). The work is further focused on fly ashes, as they constitute the vast and more active majority of Greek SCM. The effectiveness of the Greek fly ashes in concrete improvement is widely proved through strength and durability measurements at laboratory and pilot-plant scale. However, they contain high amounts of free lime and sulphates, which may cause durability problems. In addition, they exhibit inadequate fineness and composition variations. Thus, an appropriate treatment is required and proposed by the present study in order to eliminate or reduce any harmful factors. Finally, a mix design strategy ensuring optimum strength, durability and ecological profile is proposed. (A) "Reprinted with permission from Elsevier".

In this paper, the effect of metakaolin on concrete properties is investigated. A poor Greek kaolin was thermally treated at defined conditions, and the produced metakaolin was superfine ground. In addition, a commercial metakaolin of high purity was used. Eight mixture proportions were used to produce high-performance concrete, where metakaolin replaced either cement or sand in percentages of 10% or 20% by weight of the control cement content. The strength development of metakaolin concrete was evaluated using the efficiency factor (k-value). The produced metakaolin as well as the commercial one imparts a similar behavior with respect to the concrete strength. Both metakaolins exhibit very high k-values (close to 3.0 at 28 days) and are characterised as highly reactive pozzolanic materials that can lead to concrete production with an excellent performance.

Many solid industrial by-products such as siliceous and aluminous materials (fly ash, silica fume, slags, etc.) as well as some natural pozzolanic materials (volcanic tuffs, diatomaceous earth, etc.) may be characterized as supplementary cementing materials (SCM) as they exhibit cementitious and/or pozzolanic properties. Due to plenty of these materials and their large variations on physical and chemical composition, the development of a general design for their use in concrete is required. In this work, the concept of an efficiency factor is applied as a measure of the relative performance of SCM compared with Portland cement. Artificial materials of various compositions and some natural pozzolans were studied. Compressive strength and accelerated chloride penetration tests were performed. With regard to these characteristics, efficiency factors for these materials were calculated. A mix design strategy to fulfil any requirements for concrete strength and service lifetime was developed and it enables concrete performance to be accurately predicted.

For comparing the relative performance of various supplementary cementing materials (SCMs: silica fume, fly ash, slag, natural pozzolans, etc.) as regards Portland cement, the practical concept of an efficiency factor may be applied. The efficiency factor (or k value) is defined as the part of the SCM in an SCM-concrete that can be considered as equivalent to Portland cement. In the present work, an alternative procedure for experimental determination of the k value is proposed, using the concept of the pozzolanic activity index. For the first time, also, the k value for equivalent strength was correlated with the active silica content of the SCM through analytical expressions. Artificial pozzolanic materials of various compositions and some natural pozzolans were studied. It was found and verified by experimental comparison that these expressions are valid only for artificial SCMs (fly ash, slag), whereas in the case of natural SCMs the k value is overestimated. Thus, knowing primarily the active silica content of the SCM, a first approximation of the k value can be obtained and, further, the strength of a concrete incorporating artificial SCM can be predicted.

The effect of lime putty addition on main structural and durability properties of concrete was studied. Different types of cement were used for concrete preparation: a Portland cement, a pozzolanic cement and a Portland cement with the addition of 20% fly ash. The measured concrete properties were compressive strength, setting times, length change, porosity, carbonation depth and degree of steel bar corrosion. It was found that the lime putty addition has a positive effect on the properties of concrete that contain pozzolans and a slightly negative effect on the properties of pure Portland cement. This behavior was correlated with the availability of active silica of cementitious materials. The active silica of pozzolans reacts with the added calcium hydroxide giving constituents, which improve the concrete stability and durability.

A typical low-calcium fly ash was used as additive in mortar, replacing part of the volume either of Portland cement or aggregate. The development of the strength, heat, porosity, bound water, and calcium hydroxide content was measured. In aggregate replacement higher strengths were observed after 14 days, whereas in cement replacement higher strengths were observed after 91 days. The final strength gain was found to be roughly proportional to the content of active silica in the concrete volume. Bound water content and porosity results showed that fly ash reacts with calcium hydroxide, binding small amounts of water. On the basis of the experimental results, a simplified scheme describing the chemical reactions of the low-calcium fly ash in hydrating cement is proposed. Using the reaction stoichiometry, quantitative expressions for the estimation of the chemical and volumetric composition of a fly ash concrete are proposed. The model expressions can be applied in mix design and concrete performance prediction.

In this work the durability of Portland cement systems incorporating supplementary cementing materials (SCM; silica fume, low- and high-calcium fly ash) is investigated. Experimental tests simulating the main deterioration mechanisms in reinforced concrete (carbonation and chloride penetration) were carried out. It was found that for all SCM tested, the carbonation depth decreases as aggregate replacement by SCM increases, and increases as cement replacement by SCM increases. The specimens incorporating an SCM, whether it substitutes aggregate or cement, when exposed to chlorides exhibit significantly lower total chloride content for all depths from the surface, apart from a thin layer near the external surface. New parameter values were estimated and existing mathematical models were modified to describe the carbonation propagation and the chloride penetration in concrete incorporating SCM.

Silica fume was used as additive in mortar, replacing part of the volume of either Portland cement or aggregate. In a series of experiments, the development of the strength, porosity, bound water, and calcium hydroxide content was measured. The silica fume addition in both cases gave higher strengths than the control mixture. The bound water content and porosity were finally the same as for the control mixture in the case of the aggregate replacement. On the basis of the experimental results, the chemical reaction of the silica fume in hydrating cement is proposed. Using this equation and the cement hydration reactions, quantitative expressions for estimation of the chemical composition, porosity, and, indirectly, strength and durability of a silica fume–concrete are proposed.

The paper describes the physicochemical processes of concrete carbonation and presents a simple mathematical model for the evolution of carbonation in time, applicable under constant relative humidity higher than 50%. The model is based on fundamental principles of chemical reaction engineering, and uses as parameters the ambient concentration of CO2, the molar concentratrations of the carbonatable constituents, Ca(OH)2 and CSH, in the concrete volume, and the effective diffusivity of CO2 in carbonated concrete. The latter is given by an empirical function of the porosity of hardened cement paste and of relative humidity, derived from laboratory diffusion tests. The validity of the model for OPC or pozzolanic cement concretes and mortars is demonstrated by comparison of its predictions with accelerated carbonation test results obtained in an environment of controlled CO2 concentration, humidity and temperature. The mathematical model is extended to cover the case of carbonation of the coating-concrete system, for concrete coated with a cement-lime mortar finish, applied either almost immediately after the end of concrete curing or with a delay of a certain time. Parametric studies are performed to show how the evolution of carbonation depth with time is affected by cement and concrete composition (water/cement or aggregate/cement ratio, percentage OPC or aggregate replacement by a pozzolan), environmental factors (relative humidity, ambient concentration of CO2), the presence and the time of application of a lime-cement mortar coating and its composition (water/cement, aggregate/cement and lime/cement ratios of the mortar, percentage OPC or aggregate replacement by a pozzolan).

The durability of reinforced concrete is influenced by those physical characteristics of concrete that control the diffusion of gases, such as CO2 and O2 or of liquids (mainly water) through its pores, and the diffusion of ions, such as Cl-, dissolved in the pore water. These physical characteristics depend on the composition of concrete, the chemical composition and type of cement, and the relative humidity and temperature of the environment. In the present paper, these characteristics of concrete are determined analytically and/or experimentally in terms of the composition parameters and environmental condtions; the molar concentration of those constituents that are susceptible to carbonation; the porosity and pre-size distribution; the degree of saturation of the pores; and effective diffusivity of gases through the concrete.

The physicochemical processes in concrete carbonation are presented and modeled mathematically. These processes include the diffusion of CO2, in the gas phase of concrete pores, its dissolution in the aqueous film of these pores, the dissolution of solid Ca(OH)2 in the water of the the pores, the diffusion of dissolved Ca(OH)2 in pore water, its ultimate reaction with the dissolved CO2, and the reaction of CO2 with CSH and with the yet unhydrated C3S and C2S. In addition, the parallel processes of production of materials susceptible to carbonation during the hydration and carbonation, are included in the model.