Volume 6Enero - Diciembre 2016

Sergio Lobo Aguilar, Richard E. Christenson (Author)

Numeric Study of the Influence of the Signal Noise, Location of the Sensors and Sampling Rate on the Strain-Only Bwim Method

• PDF (Spanish)

Bridge Weigh-In-Motion (BWIM) systems have been used successfully to identify some of the properties of the trucks that travel over a highway. However, is not always easy to control the sources of uncertainty and therefore the reliability of the results might be affected. In this research, the effect of possible experimental difficulties on the BWIM method based on strain measurements was studied. In particular, three effects were analyzed: the noise level present on the signal, the location of the sensors on the bridge and the sampling rate used for data acquisition. These effects were modeled numerically by adding synthetic noise to an idealized wave response. The results are discussed with focus on the possible consequences on the estimation of velocities and gross vehicle weight of truck during field tests.

Hector Luis Delbono (Author)

Size Reduction Method for Laboratory Testing in Hot Mix Asphalt

• PDF (Spanish)

In a multilayer system, as a pavement with layers of different materials, movements between layers are an important source of cracks. When the adhesion between layers is poor, often cracking appear early with increasing deformation at the loads of traffic due to consumption of internal energy of the material, causing problems fatigue cracks from top to bottom (top- down).

In this context the study of adherence between different substrates (base concrete and asphalt base), interposing different geosynthetic materials, using as a bonding agent a modified asphalt emulsion, and placing thereon a layer of conventional asphalt CAC D20, acting as reinforcement in rehabilitating deteriorated of pavements was proposed. It is considered as a reference intercoat adhesion without placing any geosynthetic material.

To quantify the adhesion it was used strength test cut LCB (Laboratorio de Caminos de Barcelona), and the adhesion test traction implemented in the LEMaC, Highway Research Center of the National Technological University of La Plata is used. The load and deformation at the interfase of materials, were tested and a result it was observed that adhesion is favorably or unfavorably affected, depending on the type of geosynthetic material and the substrate where it is applied.

Eduardo José Montalto Bolaños, Yi Cheng Liu Kuan (Author)

Ambient Vibration Test of a Prestressed Concrete Box Girder Bridge

• PDF (Spanish)

This paper presents the results of an off-line vibration based monitoring of a simply-supported, prestressed concrete box girder bridge. The structure evaluated was the Tenorio River Bridge in National Route 1, Costa Rica, which was built in 2014. The purpose of the study was to register the dynamic response of the bridge under operational conditions and to identify its vibration modes using the covariance driven stochastic subspace identification method (SSI – COV). The ambient vibration test was carried out using a hybrid monitoring system developed by LanammeUCR. Uniaxial accelerometers were used to register the accelerations at 25 different locations on the bridge for approximately 40 minutes. Through the analysis of the data, nine vibration modes were identified in the frequency range of 0 to 25 Hz, including vertical bending modes, torsional modes and one transverse bending mode.

Bryan Calderón Jiménez, Jimmy Venegas Padilla, José Pablo Sibaja Brenes, Jorge Salazar Delgado, Ellen Rodriguez Castro (Author)

Determination of Total Content of Lead, Chromium, and Mercury at Trace Levels in Cement Matrix Using FAAS, GFAAS, and CVAAS: Validation of the Method

• PDF (Spanish)

This study shows the validation process for the determination of total trace concentration of lead (Pb), chromium (Cr) and mercury (Hg) in cement matrix using analytical techniques FAAS, GFAAS and CVAAS. The proposed digestion method consisted in a multistage microwave digestion, which showed the capability to dissolve all the sample (0,5 g) in 3,5 h without the presence of particles or remain solid. The linearity of the methods FAAS, GFAAS and CVAAS were corroborated using ordinary least square model (OLS) and using a graphical interpretation of the residuals from the calibration curve. The homoscedasticity of the variance was demonstrated using the Bartlett test. The results show a good agreement and excellent results in terms of linearity of the methods. The sensitivity of the calibration curves remained invariant over the time. The methods showed a small increase of the repeatability and intermediate repeatability comparing with the obtained for aqueous matrix. However, the repeatability components are less than 4 % and 6 %, respectively. The results also showed how the matrix effect, as a source of error in the determination of Cr and Pb by FAAS, was reduced using deuterium lamp as a background correction. The recoveries obtained for FAAS methods were 106.5 % for Pb and 90.5 % for Cr. The Pb and Hg were measured using GFAAS and CVAAS. These methods obtainded a 100% of recovery of the element tested. The LOD obtained in this validation show reach levels of 0.016 mg kg-1 for Cr (FAAS), 0.064 mg kg-1 for Pb (AAS), 8.72 μg kg-1 for Pb (GFAAS) and 0.43 μg kg-1 for Hg (CVAAS). Finally, the uncertainty of these methods had a low impact in the measurement, having in relative terms a level of 3.95 %, 2.28 % y 13.27 % for Pb, Cr and Hg, respectively. It is concluded that these methods show a good performance to measure metals, specifically Pb, Cr and Hg in the cement matrix, if some factors such as proper digestion of the samples and systematic effects correction will be consider.