Nowadays, the tracks that comprise the world railway network are estimated to contain nearly three billion sleepers, over 400 million of which are made of concrete. At the same time, over 50% of the world demand for sleepers (around 20 million units per year) was for the concrete version; and between 2% and 5% of the concrete ties that are laid on tracks every year are to replace or renew worn elements. Concrete durability, however, depends on many factors. And in this context it should be noted that the characteristics of the in-plant industrial process involved in manufacturing precast concrete units differs in a number of ways from in situ construction, vesting these units with properties that distinguish them, in terms of durability, from in situ concrete under the conditions generally prevailing on construction sites. Generally speaking, it is widely admitted that the activation process of fly ashes allows obtaining a material with similar cementing features to those characterising Ordinary Portland Cement. Actually, the alkali activation of fly ashes is a singular procedure by which the powder originated in the power plants is mixed with certain alkaline dissolution and cured under a certain temperature to make solid materials. Contrary to conventional concrete, however, this new type of concrete can attain high strength over a very short time (1 day) and do develop excellent durability properties.

Rev. ing. constr. [online]. 2007, vol.22, n.2, pp. 75-80. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732007000200001.

This paper deal with the design of shallow foundations on sands by using the Limit State Method. The Safety Theory is applied in order to obtain the safety coefficients needed for the design on friction soils. The Checkup of the Pressure Linear Limit is implemented, and the results obtained are compared with the safety coefficients of the Cuban Standard. The coefficients obtained in this work make possible more economic .

Rev. ing. constr. [online]. 2007, vol.22, n.2, pp. 81-88. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732007000200002.

Managing large capital construction projects requires the coordination of a multitude of human, organizational, technical, and natural resources. Quite often, the engineering and construction complexities of such projects are overshadowed by economic, societal, and political challenges. The ramifications and effects, which result from differences between early project cost estimates and the bid price or the final project cost, are significant. Over the time span between the initiation of a project and the completion of construction many factors influence a project's final costs. This time span is normally several years in duration but for highly complex and technologically challenging projects, project duration can easily exceed a decade. Over that period, changes to the project scope often occur. The subject here is a presentation of strategies that support realistic cost estimating. Through literature review and interviews with transportation agencies in the U.S. and internationally the authors developed a database of the factors that are the root causes of cost estimation problems

grandes y complejos. Rev. ing. constr. [online]. 2007, vol.22, n.2, pp. 91-98. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732007000200003.

After tunnel fire catastrophes at the end of the 1990's, the safety at road tunnel operations has become a priority on transportation policies at international level especially inside the European Union. This circumstance has required the analysis and risk assessment in those tunnels that for their special characteristics it is highly recommended. This article presents a biographical review in the topic along with a research of risk assessment models for road tunnels. The main conclusion of this study is the need of applying probabilistic models complemented by determinist studies centred in cases which may present biggest losses to the society.

Rev. ing. constr. [online]. 2007, vol.22, n.2, pp. 101-110. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732007000200004.

The present study carried out a characterization of the components of a binary blend comprised of lime-cane sugar straw ash by means of the analytic techniques ofray-x diffraction, chemical, and granulometric analysis. The evolution of the setting process of this binary blend was assessed, and it appears as an alternative mineral active addition to cement. The statistical parameters of granulometric curves of the lime, the cane straw ash and the pozzolanic blend (lime: ash = 3:7) provide criteria for mixing the blend components fitting the small grains (<9um) in the voids formed by bigger grains (45 um). The right size combination can create a space of enhanced reactivity providing compressive strengths of 13 MPa at the age of 28 days

Aglomerante puzolánico formado por cal y ceniza de paja de caña de azúcar: la influencia granulométrica de sus componentes en la actividad aglomerante. Rev. ing. constr. [online]. 2007, vol.22, n.2, pp. 113-122. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732007000200005.

In this paper the effect of the ambient relative humidity at service on the compressive and splitting strengths and in the modulus of elasticity of structural lightweight concretes is evaluated. Also, relationships are proposed allowing estimating these properties as a function of the ambient relative humidity and drying time. The concretes were made with two types of coarse lightweight aggregates, pumice and fly ash pellets, and with normal density fine aggregate. The concretes were subjected to two different environmental service conditions: 90% relative humidity and curing at 90% relative humidity during the first seven days and then to 50% relative humidity until the age of testing. The samples were tested at 7, 28, 60 and 90 days of age. An important deterioration of the measured properties due to the effect of the drying conditions was observed; at 83 days of drying, the compressive and splitting strength losses were on average of 20% and 15%, respectively, and of the modulus of elasticity of 40% with respect to concretes at 90% relative humidity. It was concluded that there are two main variables that can explain the loss of strength of lightweight concrete due to the effect of a dry environment. The first of them is the water-cement ratio which controls, among others, the permeability of the mortar or resistant phase. The second one is the relative content of lightweight aggregate in the concrete

Rev. ing. constr. [online]. 2007, vol.22, n.2, pp. 123-137. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732007000200006.

This paper proposes a methodology for estimating greenhouse gas emissions from road traffic. The method uses information about the cities and their growth estimates in order to model traffic by using a grav ity model. These kind of mathematical models allow study the number of trips “originated in” or “destined for” a particular area and distribute them to calculate the greenhouse gases emissions from these trips. In this way the information regarding these emissions can be used in urban planning phase and preventive and compensatory measures can be included in these processes.