A simple way to mitigate alkali-silica reaction

A possible practice to prevent disorders due to alkali-silica reaction (ASR) in concretes containing reactive aggregates is the use of chemical admixtures (lithium salts) or, more commonly, mineral admixtures such as fly ash, silica fume, ground granulated slag or metakaolin. An analysis of the literature concerning ASR revealed some papers devoted to the mitigating activity of reactive aggregate powders (RAP) when associated with their parent aggregates. These RAP result from the grinding of the reactive aggregate. To verify the efficiency of this method of mitigation, tests were performed on concrete prisms cured at 60°C and 100% R.H., using four reactive aggregates, associated or not with their RAP. The results showed that the use of RAP reduced or suppressed ASR-expansion, suppressed surface cracking and counteracted the loss of compressive strength due to ASR. If these findings are confirmed by trials on other types of aggregates, the addition of RAP would be a simple way of avoiding ASR disorders.     

Properties of inorganic polymer (geopolymer) mortars made of glass cullet

This study presents the results of experiments aiming to produce geopolymers from glass cullet, a non-traditional material compared to those usually found in the manufacture of geopolymers (e.g., metakaolin and fly ash). The study gives the principal formulation parameters affecting the behavior of glass cullet geopolymers. The glass used comes from recycled glass bottles. The parameters studied are the fineness of the glass (Blaine of 1000 to 4000 cm²/g), the temperature of synthesis (20, 40 and 60 °C), and the nature and concentration of the activation product (KOH, NaOH). The properties are evaluated in terms of compressive strength and durability. The results show that cullet of soda-glass can be used as a base material for the production of geopolymers and, contrary to metakaolin-based geopolymers, no waterglass is necessary for its setting and hardening since cullet glass already contains a high proportion of alkalis. Thermal activation at 40 or 60 °C is necessary but sufficient to obtain strength of more than 50 MPa, especially for the finer glass (4000 cm²/g). The durability of glass cullet geopolymers is affected by water conservation.     

Optimising an expansion test for the assessment of alkali-silica reaction in concrete structures

This work is part of an overall project for the reassessment of concrete structures damaged by alkali-silica reaction (ASR). The paper focuses on developing a laboratory method for expansion tests since the usual tests appear to be difficult to use in expert assessment. The development involves optimising the storage conditions and the sizes of the specimen and aggregate. A combined effect of the aggregate and specimen sizes on ASR expansion is thus pointed out: for a given mortar, the expansion is lower in small specimens than in large specimens. Therefore, the ratio ‘specimen size/aggregate size’ has to be sufficiently high to decrease this scale effect and obtain relevant measurements. The discussion proposes a method for always using comparable conditions during the expansion tests and finally suggests how this test can be optimised to provide fast and relevant results for use in structure reassessment.     

A new semantics for ACL based on commitments and penalties

In complex multiagent systems, the agents may be heterogeneous and possibly designed by different programmers. Thus, the importance of defining a standard framework for agent communication languages (ACL) with a clear semantics has been widely recognized. The semantics should be verifiable, clear, and practical. Most classical proposals (for instance, mentalistic semantics) fail to meet these objectives. This paper proposes a logic‐based semantics, which is social in nature. The basic idea is to associate with each speech act a clear meaning in terms of a commitment induced by that speech act, and a penalty to be paid in case that commitment is violated. A violation criterion based on the existence of arguments is then defined per speech act. We show that the proposed semantics satisfies some key properties that ensure that the approach is well founded. The logical setting makes the semantics verifiable. Moreover, it is shown that the new semantics is practical because it captures the dynamic of dialogues and shows clearly how isolated speech acts can be connected for building dialogues. © 2008 Wiley Periodicals, Inc.     

High-Pressure Device for Fluid Extraction from Porous Materials: Application to Cement-Based Materials

A high-pressure device, reaching an axial pressure of 1000 MPa, intended to the extraction of the pore solution of rigid and slightly porous materials, has been developed to improve the efficiency of extraction. This paper gives an application of fluid extraction from mortars made with Portland cement. It includes an experimental study of the performance of the apparatus, and an analysis of the results in terms of efficiency of extraction, repeatability of measurement, and effect of the squeezing pressure on the pore solution composition. Results shows that: (1) the squeezing efficiency using our apparatus is higher than those found in the literature; (2) the measurement uncertainty ranges between 1.5% and 14%; (3) no significant effect of pressure (up to 1000 MPa) is observed for concentrations of Ca, Na, K, and Si. This paper suggests conducting extraction at 1000 MPa, especially on old concrete or concrete made with low W / C ratios.     

Polarization-mode dispersion measurement: generalization of the interferometric method to any coupling regime

We present the theoretical framework that provides for a generalization of the standard interferometric method of polarization-mode dispersion (PMD) measurement. The basic formula linking the root-mean-square (rms) differential group delay (DGD) to the interferograms is derived independently of previous assumptions regarding the coupling regime, the shape of the interferograms, or the width and smoothness of the source spectrum. Moreover, the measured rms-DGD value is shown to be a well-defined weighted average over a finite wavelength range that can be rigorously traced to DGD measurements. Numerical simulations confirm the mathematical exactness of the analysis, and experimental tests confirm the extended range of validity provided in practice by the generalized method.     

Structural characterization of non-reductively ethylated coal by 13C and 1H n.m.r.

A major portion of some coals can be solubilized by non-reductive ethylation. A part of the solubilized portion of a bituminous highly caking coal was studied by ¹H and ¹³C nuclear magnetic resonance techniques. It was demonstrated that important structural information can be obtained by this method for the original insoluble material in coal. It was found that, in the investigated coal, about 40% of the aromatic carbon atoms are protonated and that 6–10% of total carbon atoms existed in original coal as active sites that were amenable to ethylation.     

Goal-Oriented Adaptivity and Multilevel Preconditioning for the Poisson-Boltzmann Equation

In this article, we develop goal-oriented error indicators to drive adaptive refinement algorithms for the Poisson-Boltzmann equation. Empirical results for the solvation free energy linear functional demonstrate that goal-oriented indicators are not sufficient on their own to lead to a superior refinement algorithm. To remedy this, we propose a problem-specific marking strategy using the solvation free energy computed from the solution of the linear regularized Poisson-Boltzmann equation. The convergence of the solvation free energy using this marking strategy, combined with goal-oriented refinement, compares favorably to adaptive methods using an energy-based error indicator. Due to the use of adaptive mesh refinement, it is critical to use multilevel preconditioning in order to maintain optimal computational complexity. We use variants of the classical multigrid method, which can be viewed as generalizations of the hierarchical basis multigrid and Bramble-Pasciak-Xu (BPX) preconditioners.