<select id="lBetonID">
    <option>- wybierz -</option></select>

//Lista dla betonu    
var zmsel1 = document.getElementById("lBetonID");
var zmopt1 = concrete[0].slice(2);
for(var i = 0; i < zmopt1.length; i++) {
    var opt1 = zmopt1[i];
    var el1 = document.createElement("option");
    el1.textContent = opt1;
    el1.value = opt1;
    zmsel1.appendChild(el1);
}