\name{concrete}
\alias{concrete}
\docType{data}
\title{
   Air Bubbles in Concrete
}
\description{
   Prof. Shin-ichi Igarashi's data:  a point pattern of the locations,
   in a cross-section of a concrete body, of the centroids of
   air bubbles in the cement paste matrix surrounding particles
   of aggregate.
}
\usage{data("concrete")}
\format{
  An object of class \code{"ppp"} representing the point pattern
  of air bubble centroid locations.
}
\details{
  The window of the point pattern is a binary mask
  (window of type \code{"mask"}; see \code{\link[spatstat]{owin}}
  and \code{\link[spatstat]{as.mask}} for more information
  about this type of window).
  This window in effect consists of the
  cement paste matrix, or equivalently of the complement (in the
  observed cross-section) of the aggregate.

  Major scientific interest is focussed on analysing the distribution
  of the location of the air bubbles in the cement paste matrix.
  These bubbles are important in assuring frost resistance of the
  concrete.  Each air bubble protects a region around it to a certain
  distance. To protect an entire concrete object against severe frost
  attack, it is necessary to cover the whole of the cement paste matrix
  with subsets of protected regions formed around the air bubbles. It
  is believed that the protected regions are related to the Dirichlet
  tessellation of the centroids of the bubbles, and the statistical
  properties of the protected regions can be determined from those
  of the Dirichlet tessellation.  In this regard, the areas of the
  tiles are particularly important.
}
\source{
  Prof. Shin-ichi Igarashi, of the School of Geoscience and
  Civil Engineering, Kanazawa University, personal communication.
}
\references{
  Natesaiyer, K., Hover, K.C. and Snyder, K.A. (1992). Protected-paste
  volume of air-entrained cement paste: part 1. \emph{Journal of
    Materials in Civil Engineering} \bold{4} No.2, 166 -- 184.

  Murotani, T., Igarashi, S. and Koto, H. (2019). Distribution
  analysis and modeling of air voids in concrete as spatial point
  processes. \emph{Cement and Concrete Research} \bold{115} 124 -- 132.
}
\examples{
  if(require(spatstat)) {
     plot(concrete,chars="+",cols="blue",col="yellow")
     # The aggregate is in yellow; the cement paste matrix is in white.

     # Unit of length: use \mu symbol for micron
     unitname(concrete) <- "\u00B5m"

     if(interactive()) {
       # Compute the Dirichlet tessellation
       dtc <- dirichlet(concrete)
       plot(dtc,ribbon=FALSE, col=sample(rainbow(dtc$n)))
       # Study Dirichlet tile areas
       areas <- tile.areas(dtc)
       aa <- areas/1000 # Divide by 1000 to avoid numerical instability
       # Fit a gamma distribution by the method of moments 
       mm <- mean(aa)
       vv <- var(aa)
       shape <- mm^2/vv
       rate <- mm/vv
       rate <- rate/1000 # Adjust for rescaling
       hist(areas,probability=TRUE,ylim=c(0,7.5e-6),
          main="Histogram and density estimates for areas",ylab="",xlab="area")
       lines(density(areas),col="red")
       curve(dgamma(x,shape=shape,rate=rate),add=TRUE,col="blue")
       legend("topright",lty=1,col=c("red","blue"),
              legend=c("non-parametric","gamma fit"),bty="n")
     }
  }
}
\keyword{datasets}
